======================LIGHT=======================================

mid-day Sun           at Earth's equator on clear day has a power density 
                      of about 1 KW/square meter or about 1 mW/sq.mm. 
num photons           are coming out of my laser?:
                                          1,240 nm
                      E = 1.602E-19 J * -------------
                                           lambda
                      Where: lambda is the wavelength of your light source.
                      1,240 nm is the photon wavelength with an energy of 1 ev.
                      Then, photon flux = P/E where P is the beam power.
                      For example, a 1 mW, 620 nm source will produce about:
                      1E-3 / (1.602E-19 * 2) = 3E15 photons/second.

----------------------------------------------------------------------------

100W light bulb       about 5 to 7 W of visible light (mostly IR and heat) 
                      10 cm from a 100 W bulb power density about .05 mW/sq.mm.
                      At 1 m, would only .0005mW/sq. mm or 500 mW/sq. m.  
                      Based on this 
                      back-of-the-envelope calculation,
                      a 5 mW laser beam spread out to a circular spot 
                      of .1 m diameter (1 mR divergence at 50 m - 
                      without external optics) will be brighter
                      than 100 W light bulb at 1 m!  , close to laser itsel
                      beam may be only 1 *mm* in diameter 
                      thus 10,000 times more intense!


                      color temperature is high.   
                      4000-10,000 Kelvin

----------------------------------------------------------------------------

Red LEDs              11-22+ lumens/watt by Agilent,
                      Red-Orange LEDs - 21-22 maybe now 28.5 lumens/watt by 
                      Yellow-Green LEDs - 3-4 lumens/watt 
                      Green LEDs - 25-32+ sometimes 42 lumens/watt by Nichia, 
                      Blue LEDs - 7.5-probably 8, rarely 10 lumens/watt by 
                      Voltage drop at 20 mA was mostly 3.45-3.5 volts. Estimated 
luminous efficacy     of  emitted light was mainly 450-475 lumens per watt, 
                      maybe as low as 420-440 for bluest one 
                      and as high as 520-525 for one that was
                      noticeably more of a lime green than the other 55 of the 
                      56 good pieces.
----------------------------------------------------------------------------
lumen                 is  unit of light output, equal to 1 / (60 * pi) 
                      of light emitted by one square centimeter 
                      of ideal blackbody surface at meltingpoint of platinum.
                      When  spectrum differs from that of a blackbody at  
                      melting point of
                      platinum, equate lumens by applying  official photopic 
                      function to the
                      quantity of light at every wavelength present.
----------------------------------------------------------------------------

One watt of light     at any single wavelength (or in a very narrow band) 
                      is, in lumens, 681 times  official photopic function 
                      of that wavelength. Any eyeballs (or other light
                      sensors) of spectral response deviating from that of the 
                      "official standard
                      observer" could see as unequally bright light sources of 
                      equal
                      lumens/candela and different spectral output.
                      "USA-usual" 100 watt, 120 volt, 750 hour "regular" (A19)
                      lightbulb  usually
                      produces 1710 lumens.
----------------------------------------------------------------------------

Lumens per watt       efficiency in converting electrical energy to light
                      Multiply this by watts dissipated in LED to get lumens. 
                      typical red, orange, or yellow or yellow-green LED 
                      has a voltage drop around 2 volts 
                      "standard" current of 20 milliamps.
                      blue, white, or non-yellowish-green one  3.4 volts 
                      at 20 mA and gets .068 watt at 20 mA.
----------------------------------------------------------------------------

candela               is a lumen per steradian, or "beam candlepower". 
candela               equal to 1/60 of perpendicular/normal "candlepower" 
                      of one square centimeter of ideal blackbody surface 
                      at melting point of platinum.
lumens                are candelas times the beam coverage in steradians. 
Candelas              arelumens divided by  beam coverage in steradians. 
                      Ideally, that is -
                      assuming that all light is within the beam and the 
                      "candlepower" is constant within this beam.
                      a steradian is. It is 1/(4*pi) of a whole sphere
                      or about 3283 "square degrees".
                      To get steradians from the beam angle:
                      Steradians = 2*pi*(1 - cos(.5*(beam angle)))
                      if you determine steradian beam coverage and 
                      multiply that by  candela figure 

                      brightest and most efficient LEDs and where to get 
                      them!
                      Most efficient soon-to-come red-orange - 53 lumens/watt
                      Most efficient soon-to-come red - 42 lumens/watt
                      Most efficient green - often, maybe usually 35 lumens/watt
                      Most efficient soon-to-come yellow / "amber" - nearly 35 
                      lumens/watt
                      Most efficient soon-to-come white - 20 to maybe 25 
                      lumens/watt
                      Most efficient soon-to-come blue - 12 lumens/watt
                      For comparison:
                      USA usual 100W "A19" incandescent - 17.1 lumens/watt.
                      Compact fluorescents - mostly 45-60 lumens/watt including 
                      ballast losses.
                      32 watt T8 fluorescent in "average condition" - typically 
                      around 80
                      lumens/watt including ballast losses.
----------------------------------------------------------------------------


Neon indicator lamps  low density neon gas in a sealed container. A 
                      voltage, related to the distance between 
                      electrodes (small in the first case, large in
                      second) "breaks down" (ionizes) neon[1]. As  
                      electrons fall back,radiate in visible, 
                      color characteristic of gas.
                      Ionized gases had negative resistance (really),
                      so without a limiter, they would
                      destroy themselves or the supply. In case transformer, 
                      typical US values are around 6,000VAC and up at few mA.
                      display work,combinations of gases used to get
                      variant colors.Some colors also from colored glass tubing.
                      sufficiently high (circa 90V) voltage ionizes neon gas
                      and makes it conductive. 
                      Once it's ionized a lower voltage will keep it
                      ionized and keep current flowing through the lamp. 
                      only other component involved is series resistor to
                      limit the current to something like a few milliamps.
                      If mean fancy store signs,involved is a
                      high voltage transformer. "breakdown" voltage must be 
                      much higher (10's of KV)
                      because two electrodes meters apart instead of 1 mm apart.
                      Different colors from different combinations of gases.
                      Neon lamps and neon signs are filled with fairly low 
                      pressure gas. not vacuum, but much lower than atmospheric 
                      Neon lights  filled with an inert gas like neon, argon,
                      xenon, krypton... (noble gases). There is a cathode and 
                      anode, usually one at each end of the tube.
                      The Inner Workings
----------------------------------------------------------------------------

fluorescent tube      is a glass tube [1] filled with a low pressure mixtures
                      of gases among which are mercury and argon.
                      At each end ofthe tube are two electrodes [2] 
                      with are connected by a filament [3] inside  tube.
                                       [1]
                         --------------------------------------------- - - - -
                         ||+++++++++++++++++++++++++++++++++++++++++++
                         ||                              [4]
                       --||---/
                   [2]   ||   \  [3]
                       --||---/
                         ||                              [4]
                         ||+++++++++++++++++++++++++++++++++++++++++++
                         --------------------------------------------- - - - -
                      The inside of the tube is coated with a layer of 
                      fluorescent material [4].
                      mercury atoms give off ultraviolet light, causing [4] to 
                      emit visible light.
                      following circuit is used get tubes to "light up"
                         [1] ~-----------
                                        |
                                        |
                                        )|
                                        )| [2]
                                        )|
                                        )|
                                        |    -------------------------
                                        |    |            |          |
                                      ----------          |          |
                                      |  |  |  |          |          |
                                      |  /\/\  |          |          |
                                      |        |      [4] |          |
                                      |        |        +++++        |
                                 [3]  |        |        + S +      -----[5]
                                      |        |        +++++      -----
                                      |        |          |          |
                                      |        |          |          |
                                      |        |          |          |
                                      |  /\/\  |          |          |
                                      |  |  |  |          |          |
                                      ----------          |          |
                                        |    |            |          |
                                        |    -------------------------
                                        |
                        [1] ~------------
                      When mains voltage [1] is applied to the circuit, the 
                      starter [4] (which is
                      basically a switch) allows current to flow through the 
                      electrodes of the
                      tube [3]. The current causes the starter's contacts to 
                      heat up and open,
                      thus interrupting the flow of current. This causes a great 
                      increase in
                      voltage in the inductor [2] (called a ballast here, in the 
                      UK & US too I
                      presume :-) which eventually (it doesn't always work first 
                      time!) causes the
                      tube to light. Since the gases in the tube have negative 
                      resistance, the
                      inductor now plays the role of a current limiter. The 
                      capacitor [5] is
                      sometimes used to get voltage and current back in phase.
                      On smaller fluorescent tubes and lamps (i.e. the ones you 
                      can plug in to
                      incandescent lamp sockets) the inductor is sometimes 
                      replaced by a resistor.
                      Additional Info
                      I thought I'd share some more data from the Elektor 
                      article with you...
                      + Light output: incandescent lamps output around 10 to 20 
                      lm/W whereas some
                      of the tubes (generally the biggest ones) give off up to 
                      70 lm/W. Thus
                      showing that the tubes are cheaper to run than 
                      incandescent lamps.
                      + Lifetime: the lifetime of fluorescent tubes and lamps 
                      depends greatly on
                      their mean "on-time" (i.e. how long they are emitting 
                      light for on average).
                      Mean on-time (hours) Mean lifetime (h) Mean lifetime (h)
                                        Fluor. tubes        Fluor lamps
                      .25                 2500                1250
                      .5                  5000                2500
                      1                   7000                3500
                      2                   9000                5000
                      5                  12000                6500
                      10                 14000                7500
                      incandescent lamps  have a mean lifetime of around 1000 
                      hours, irrespective of on-time)
                      +  0.000000e+00mitted light:
                      in fluorescent lamps the %age of light they emit
                      depends not only on their age but also on the ambient 
                      temperature and on
                      their orientation! For instance, fluor. lamps of around 
                      10W power give off
                      1000f light at 10 degrees celsius when they are 
                      "pointing upwards" (i.e.
                      vertically mounted and socket being the lowest part of the
                      lamp). At 40C 
                      same lamp would only emit at 80 0.+00fficiency. If same 
                      lamp  lying sideways it gives off 100% light 
                      at around 25C but only 70% at 10C. Don't
                      ask me why, they didn't say... but I'd like to know if 
                      this is true or not
                      (and also why!).
                      Well, that's all folks. Thanks again for all the info, I 
                      hope some of this
                      is useful to you. Oh, and BTW, the "Additional Info" part 
                      is *not* meant to
                      start another of our periodical "bulb wars", don't flame 
                      me for it, and,
                      yes, I too wish that Elektor had listed their sources of 
                      data.
                      All the best,
                      Paul.
                      --
                      
                      >flourescent tubes may not be run in series,
                      t on 220-240v supplies, what you suggest is
                      actually very common for tubes up to 40W. However, each 
                      tube has it's ownstarter, ballast  specially designed for 
                      the purpose...
                                        ____________        _____________
                     ----uuuuuuuu------|            |------|             |-----
                         ========     -|____________|-    -|_____________|-
                         ballast     |       _        |  |        _        |
                                      ------(_)-------    -------(_)-------
                                          starter              starter
                      In most tube failure modes, death of one tube will prevent
                      other from working too.
                  
                      Wiring for preheat fluorescent fixtures:
                      The following is the circuit diagram for a typical preheat 
                      lamp - one that
                      uses a starter or starting switch.
                                    Power Switch    +-----------+
                       Line 1 (H) o------/ ---------|  Ballast  |-----------+
                                                    +-----------+           |
                                                                            |
                                            .--------------------------.    |
                       Line 2 (N) o---------|-       Fluorescent      -|----+
                                            | )         Tube         ( |
                                        +---|-         (bipin)        -|----+
                                        |   '--------------------------'    |
                                        |                                   |
                                        |          +-------------+          |
                                        |          |   Starter   |          |
                                        +----------| or starting |----------+
                                                   |   switch    |
                                                   +-------------+

----------------------------------------------------------------------------

Green and White       Neon Lamps
                      These resemble neon lamps, but have a white phosphor 
                      coated onto  inside surface of the bulb.
----------------------------------------------------------------------------
 

Spectrum Tubes        Spectrum tubes are basically short "neon" tubing. more 
                      popular "Plucker"
                      tube found in high school and college science labs.  
                      about a foot (30 cm) long. central portion is about a 
                      third of this
                      length and is quite narrow, about 6 mm. (1/4 inch) in 
                      outside diameter and
                      one or two millimeters inside diameter. end portions 
                      are about a half
                      inch (13 or so mm.) in diameter and resemble those of 
                      "neon" tubing. These
                      tubes come with any of several gases and vapors, and are 
                      used with a
                      spectroscope to demonstrate the spectra of these gases.
                      Similar are "Geissler tubes", which have larger, sometimes
                      coiled centralportions.
                      The Plucker tubes require a few thousand volts with 
                      current limited to a few
                      milliamps.Special power supplies for these are available, 
                      but generally
                      expensive. An alternative is a neon sign transformer with 
                      a reduced voltage
                      (about a quarter to half of normal) applied to its 
                      primary. These tubes also
                      usually work well with Tesla coils. It is generally 
                      recommended to not have
                      the average current exceed about 5 or 10 milliamps or so. 
                      Peak currents
                      should generally be kept under 100 mA,preferably under 40 
                      mA to minimize
                      sputtering of the electrodes.
                      Extreme peak currents of many amps will make many of these
                      gases glow a
                      light blue or blue-white color, but the electrodes were 
                      not designed to make
                      these tubes work as flashtubes. Any attempt at "flashtube"
                      operation should
                      be done sparingly and with low energy levels, preferably 
                      well under a joule.
                      Tubes containing hydrogen, helium, neon, argon, krypton, 
                      xenon, and mercury
                      vapor (probably combined with one of the noble gases) are 
                      suitable for
                      extensive experimental and demonstration use. Tubes with 
                      other gases
                      (especially air, oxygen, water vapor, or ESPECIALLY any of
                      the halogens) are
                      more prone to internal corrosion and should be used 
                      sparingly and not
                      expected to have a good life expectancy. The neon tube is 
                      the brightest of
                      these and costs about 15, maybe 26 US$. These tubes are 
                      available at Edmund
                      Scientific (1-609-573-6250) and some other scientific 
                      equipment suppliers.
                      Typical colors associated with various gases:
                      Hydrogen - Lavendar at low current, hot pinkish magenta if
                      the peak current
                      is near or over 10 mA.
                      Helium - Whitish orange. Has been reported to be grayish, 
                      bluish, or
                      green-bluish white under some conditions, but I have not 
                      seen this.
                      Neon - Red-orange.
                      Argon - Violetish lavendar. Bright light blue at extreme 
                      peak currents.
                      Nitrogen - Similar to argon, slightly duller and often 
                      slightly more
                      pinkish. Bright bluish white, usually whiter than argon, 
                      at extreme peak
                      currents.
                      Oxygen - Violet-lavendar, dimmer than argon.
                      Krypton - Grayish dim off-white, may have some greenish 
                      tint. Bright
                      blue-white at extreme peak currents. (I have not seen this 
                      gas glowing in
                      this tube, but I have seen krypton glowing elsewhere.)
                      Mercury Vapor - Light blue.
                      Xenon - Grayish or blue-grayish dim white. Very bright 
                      green-bluish white at
                      extreme peak currents, more green-blue in this tube than 
                      is typical of most
                      flashtubes.
                      Water Vapor - Similar to hydrogen but dimmer.
                      Carbon Dioxide - Slightly bluish white, brighter than 
                      xenon unless peak
                      current is really high.
                      Electroluminescent/"Limelight"/"Californeon"/"Indiglo" 
                      lights
                      An electroluminescent lamp is basically a capacitor with a 
                      "lossy"
                      dielectric that includes some sort of phosphor to make 
                      light from part of
                      the dielectric loss. They must have AC, or at least very 
                      unsteady DC, in
                      order to work. These typically require somewhat high 
                      voltages. A minimum of
                      something like 20 volts or so is needed to make them work, 
                      and these
                      typically use 100-140 volts AC, up to 200 volts if the 
                      waveform is a square
                      wave. At power line frequencies of 50-60 Hz, 
                      electroluminescent lamps are
                      not bright, but last several years. To get more 
                      brightness, AC of higher
                      frequencies of a few hundred Hz (possibly even a few KHz?) 
                      is needed.
                      The "Lime Light" is an electroluminescent night light that 
                      has an appearance
                      something like a miniaturized TV set (with no controls, 
                      speaker, antenna,
                      etc). It consumes some very small amount of power (I 
                      forget exactly) like
                      about 1/16 watt. The screen glows with a slightly whitish, 
                      maybe slightly
                      bluish shade of green roughly like that of many green 
                      traffic lights. The
                      light output is a bit more than that of NE-2G green neon 
                      lamps, easily
                      enough to illuminate even a large room or two for night 
                      vision. The luminous
                      efficiency is comparable to that of incandescent lamps, 
                      although much higher
                      for night vision.
                      "Californeon" is a name for flexible electroluminescent 
                      strips that can be
                      worn by cyclists, joggers, Trick-or-treaters, partyers, 
                      etc. These come with
                      an inverter that produces the necessary high voltage 
                      higher frequency AC
                      from batteries. I believe these are the bright, slightly 
                      whitish green
                      things I have seen before.
                      For more info on the web for "Californeon", go to 
                      Altavista
                      (http://www.altavista.com) and do a simple search on 
                      californeon. You will
                      get about a hundred hits including some places that sell 
                      this stuff.
                      Other suppliers of electroluminescent stuff include:
                      Flatlite.
                      Neontrim, which sells electroluminescent "wire".
                      Coollight, another supplier of "neon wire".
                      Elam, a manufacturer.
                      Some LCD computer screens used in laptop computers have 
                      electroluminescent
                      backlights. These usually glow with a color roughly like 
                      that of a "cool
                      white" fluorescent lamp. An inverter is used to supply AC 
                      with a voltage
                      around 100 volts or more and a frequency in the hundreds 
                      of Hz or maybe one
                      or two KHz. Some miniaturized TV sets also have 
                      electroluminescent
                      backlights. So do a few building entry intercoms and maybe 
                      other things with
                      LCD displays.
                      "Indiglo" is a brand name of smaller electroluminescent 
                      lighting devices
                      used in some watches and a nightlight and maybe a few 
                      calculators and the
                      like.
                      Some smaller screens have LED backlights.
                      Many computer screens and maybe a few TVs have fluorescent 
                      backlights. If
                      you have a spectroscope, or even a diffraction grating or 
                      a CD to use as a
                      diffraction grating (requires practice), you can tell the 
                      difference.
                      Fluorescent lamps emit a spectrum containing mercury lines 
                      as well as the
                      spectrum of the phosphor (which varies). The mercury 
                      spectrum has
                      significant lines in the yellowish green and violetish 
                      blue, and weaker
                      lines in the yellow and deep violet. Phosphor spectra 
                      vary, sometimes
                      basically continuous and spanning most of the visible 
                      spectrum, sometimes
                      consisting of bands. A few phosphor bands have been known 
                      to be very narrow,
                      resembling lines. Such is the orange-red line/band found 
                      in the spectra of
                      most compact fluorescent lamps.
                      Low Current Red LEDs
                      These are the first commercially successful variety of 
                      high efficiency red
                      LEDs, becoming widely available in the mid or late 1970's. 
                      Unlike the more
                      recent types of high efficiency red LEDs, these are 
                      efficient only at low
                      currents of a few milliamps or less. The brightness is 
                      noticeably less than
                      proportional to current as current increases above about 2 
                      to 4 milliamps.
                      Low current red LEDs are made with gallium phosphide doped 
                      with zinc oxide.
                      Other gallium phosphide LEDs glow green or yellow-green.
                      The spectrum of low current red LEDs is broad, including 
                      the entire visible
                      red portion. Spec sheets often indicate a rather long peak 
                      wavelength around
                      690 nM, but this may be at low currents. The spectrum and 
                      color change with
                      current, and usually seems to be mostly red wavelengths 
                      shorter than 690 nM.
                      The color may be orange rather than red at currents around 
                      20-30 mA, and the
                      different color does not alone indicate any damaging 
                      conditions or
                      overheating to the LED. When the color is orangish, a 
                      minor secondary
                      spectral band appears in the green around 550-560 nM.
                      Most other LEDs are most efficient at currents over 10 
                      milliamps. However,
                      silicon carbide blue LEDs (without gallium nitride) are 
                      also most efficient
                      at low currents. Indium gallium nitride ultrabright green, 
                      blue and white
                      LEDs are also most efficient at lowish currents of a few 
                      milliamps.
                      "Neon" tubing that changes color
                      In a few places, you might find what looks like neon 
                      tubing, but it is
                      dimmer and the color changes. The color typically cycles 
                      through some
                      sequence of different colors.
                      The tubing is actually a "light pipe", which is usually a 
                      solid rod of
                      transparant material or a bundle of optical fibers. Light 
                      that enters an end
                      of a transparant rod can totally reflect back into the rod 
                      every time it
                      hits the side, if its angle is more parallel to the axis 
                      of the rod than
                      some critical angle. The rod/"tubing" for the color 
                      changing "neon" is
                      slightly roughened, sanded, diffused, or otherwise made 
                      slightly "leaky".
                      The light entering the rod goes through (typically) some 
                      sort of mechanism
                      of colored filters, probably some sort of rotating wheel 
                      with different
                      color filter gels. The light source is, at least 
                      sometimes, a metal halide
                      lamp.
                      There is another technology for color-changing neon 
                      tubing. The tubing in
                      this case is actual gas discharge tubing, and the waveform 
                      applied is
                      varied. The tubing has different ingredients. One waveform 
                      with a low peak
                      current favors one color, and another waveform with a high 
                      peak current
                      favors another color. For a little more info, check out:
                      http://www.multineon.com.
                      Neodymium bulbs
                      A neodymium bulb is an ordinary incandescent light bulb, 
                      except that the
                      bulb is made of a special bluish glass known as neodymium 
                      glass. Unlike
                      other light blue filter materials that slightly attenuate 
                      a broad range of
                      the spectrum from green through red, neodymium glass has a 
                      narrow absorption
                      band in the yellow and yellow-orange. A neodymiub bulb 
                      glows with a whiter
                      color like that of some halogen lamps.
                      The special effect of the neodymium glass filtering is to 
                      achieve more red
                      and green output than usual for a light source of a given 
                      brightness and
                      overall color. This causes red and green objects to look 
                      slightly brighter
                      and more intensely colored than usual. The "triphosphor" 
                      type fluorescent
                      lamps, including most compact fluorescent lamps, have a 
                      similar effect
                      except that the fluorescents make bright pure reds look 
                      slightly orangish.
                      Neodymium bulbs are dimmer than unfiltered incandescent 
                      bulbs of the same
                      wattage and life expectancy. Neodymium bulbs do not have 
                      increased output at
                      any wavelength, except for an infrared band around 1064 nM 
                      where neodymium
                      glass fluoresces.
                      Neodymium bulbs are available as the General Electric 
                      "Enrich" 60 and 40
                      watt bulbs At K-Mart and many other places where GE 
                      lightbulbs are sold.
                      Other neodymium bulbs including other wattages are 
                      available from a few
                      hardware stores, a few lighting/electrical supply shops 
                      and the like as well
                      as a few companies offering high-priced premium 
                      daylight-like light sources,
                      where the prices include hype including but not 
                      necessarily limited to
                      health claims. Bulbs.com has a couple models. Major 
                      manufacturers include
                      Bulbrite and Chromalux.
                      Tungar bulbs
                      Tungar bulbs are gas filled low voltage, high current 
                      rectifier tubes. The
                      name refers to the fact that some are argon filled and 
                      have a tungsten
                      filament cathode. There are mercury vapor versions of 
                      these also. Tungar
                      bulbs were often used in car battery chargers before 
                      silicon diodes became
                      available. Tungar bulbs typically rectified a few amps and 
                      had peak reverse
                      voltage of a few tens of volts, and a forward voltage drop 
                      of maybe around
                      10 volts.
                      The cathode typically required about 1.5 volts at around 
                      15 amps. Some
                      mercury vapor models have more complex cathode structures 
                      that sometimes
                      trapped mercury, and the cathode drew even nore current 
                      for several seconds
                      to maybe a minute until the mercury was vaporized from the 
                      cathode structure
                      and the cathode reached normal operating temperature.
                      In operation with current flowing from cathode to anode, 
                      argon filled models
                      had a dim "fuzzball" of violetish colored glow around the 
                      filament. At least
                      in some models, the filament was so much brighter that the 
                      argon glow was
                      nearly invisible. Argon has a way of being unexpectedly 
                      dim at currents
                      around a few tenths of an amp to several amps. In mercury 
                      vapor models, the
                      glow is light blue and brighter. In at least one mercury 
                      model with a more
                      complex cathode structure and two anodes, the cathode has 
                      a dim red-orange
                      glow that is invisible through the brighter blue mercury 
                      glow. The mercury
                      glow also has a strange pattern, making this bulb possibly 
                      useful for
                      B-grade science fiction movies.
                      Bulbs with purple/pink/orange-pink flowers/birds and green 
                      leaves
                      These light bulbs are most often approx. 3-1/8 inches 
                      (approx. 8 cm.) in
                      diameter, and have one of the following:
                      Two roses glowing pink or pink-orange and leaves that glow 
                      green.
                      A flamingo that glows pink or pink-orange and leaves that 
                      glow green.
                      Two orchids that glow dim violet with leaves that glow a 
                      brighter green.
                      Now there are other forms, but the three above are most 
                      common.
                      The birds/flowers are covered with a glow discharge like 
                      that of neon glow
                      lamps. The bulbs are filled with a gas mixture that is 
                      tailored to provide
                      some shortwave ultraviolet to cause a green-glowing 
                      phosphor on the leaves
                      to glow green.
                      Pink or pink-orange glow in these bulbs is achieved with a 
                      mixture of neon,
                      argon, and krypton but mostly neon. The neon-argon mixture 
                      is a little more
                      argon-rich than that optimized for easiest starting (maybe 
                      a few percent
                      argon). The argon adds some violet and violet-blue 
                      spectral content to make
                      the glow more pink and less orange. Some krypton is added 
                      to add some
                      visible blue-violet spectral content and some 
                      very-short-wave UV.
                      It is interesting to note that a 99.5 percent neon, .5 
                      percent argon mixture
                      is popular in some neon lamps as a "Penning" mixture that 
                      ionizes more
                      easily than neon or argon alone. The cathode glow in these 
                      lamps is orange,
                      in fact more yellow than the color of pure neon. The 
                      "electron temperature"
                      is reduced, and the spectral output is shifted away from 
                      all visible lines
                      and towards the infrared argon lines. The violet and 
                      violet-blue argon lines
                      are extremely weak here. For some reason, the strongest 
                      yellow line of neon
                      is weakened less than other neon lines are, making the 
                      neon color more
                      yellow. In lamps with 99.5 percent neon, .5 percent argon 
                      and a main
                      discharge column (such as many sodium lamps when first 
                      started), the color
                      is more magenta than that of pure neon.
                      In the bulb with violet orchids, the gas mixture is argon 
                      and xenon. The
                      visible spectral output is almost entirely that of argon, 
                      and the glow is
                      argon violet. The xenon produces very-short-wave UV. I 
                      have at times seen
                      the spectrum of barium from occaisional bright spots in 
                      the glow, and
                      believe the barium is a treatment to favor glow forming on 
                      particular parts
                      of the electrodes, or it may be a getter material.
                      The shortwave UV is very completely blocked by the glass 
                      bulb, and is not
                      any sort of hazard.
                      As for where to get these - Spencer Gifts, at many malls - 
                      check your phone
                      book or this link.
                      Medium Pressure Mercury Vapor Lamps
                      To some, there is no such thing as a medium pressure 
                      mercury vapor lamp. Any
                      mercury vapor lamp that is useful for anything would be 
                      either low pressure
                      (mercury vapor pressure of .000001 to .0002 atmosphere, 
                      usually plus some
                      inert gas) or high pressure (.05 atmosphere to hundreds of 
                      atmospheres).
                      However, there is a type of mercury vapor lamp usually 
                      called a medium
                      pressure mercury vapor lamp. The arc tube is quartz and 
                      anywhere from 5 to
                      as much as 77 inches (12 to 195 cm) long. The power input 
                      is high, typically
                      200 to 400 watts per inch of arc length, or 80 to 160 
                      watts per centimeter
                      of arc length. The pressure is around an atmosphere or 
                      somewhat less. So it
                      can be said that this is a specialty type of high pressure 
                      mercury vapor
                      lamp.
                      These lamps are usually used in industrial applications 
                      requiring large
                      amounts of ultraviolet, such as some graphic arts and 
                      printing applications.
                      There is a fair amount of UV in the mercury line clusters 
                      at 365-366 nM and
                      313 nM. Please note that the 313 nM wavelength is UV-B and 
                      can harm eyes and
                      cause severe sunburn. Please note that at close range, the 
                      365-366 nM UV may
                      not be completely safe to skin for prolonged exposure or 
                      for those taking
                      photosensitizing prescription drugs (ask your pharmacist). 
                      Large amounts of
                      365-366 nM UV are not completely safe for eyes.
                      Cold Cathode Fluorescent Tubes (small and large)
                      Most fluorescent tubes are of the "hot cathode" type. In a 
                      hot cathode
                      fluorescent tube, the cathode is thermionically emissive 
                      and the typical
                      "cathode fall" (voltage drop to get an electron dislodged 
                      from metal and
                      into the gas discharge) is about 10 volts.
                      There are some oddball fluorescent lamps known as "cold 
                      cathode" fluorescent
                      lamps, which are lower current ones with non-thermionic 
                      electrodes and a
                      much higher cathode fall of over 50 volts.
                      The original cold cathode fluorescent lamps were basically 
                      slightly
                      oversized white "neon" tubing with a largish diameter 
                      around 3/4 inch (20
                      mm.), and with current around or a little over 100 
                      milliamps. Most of these
                      tubes were long and U-shaped.
                      Nowadays, there are miniature cold cathode fluorescent 
                      lamps. Most of these
                      are 3 to 6.4 mm. (1/8 to 1/4 inch) in diameter and usually 
                      take a current
                      around 5 milliamps (sometimes as low as 2.5 mA). These are 
                      mostly used as
                      backlights for LCD screens in laptop computers and the 
                      like. (NOTE: Some
                      laptops use smaller standard and/or compact fluorescent 
                      lamps and some use
                      electroluminescent panels.) A few miniature cold cathode 
                      fluorescent lamps
                      are used in other applications such as solar powered lawn 
                      lights.
                      There are a few blacklight versions of miniature cold 
                      cathode fluorescent
                      lamps.
                      A major manufacturer of miniature cold cathode fluorescent 
                      lamps is JKL
                      Lamps.
                      Xenon flashlight bulbs and other xenon incandescent bulbs
                      There are some incandescent bulbs such as some flashlight 
                      bulbs with xenon
                      in them. Some halogen bulbs including some automotive 
                      headlight bulbs have
                      xenon in them also. But these are all incandescent lamps 
                      and not arc lamps.
                      There is an advantage, usually minor, in using xenon 
                      instead of the usual
                      argon-nitrogen mixture or plain argon (or sometimes 
                      krypton) in these.
                      More info on incandescent lamps with xenon are in my Xenon
                      Filled
                      Incandescent Lamp Page.
                      There are HID (electric arc) automotive headlight bulbs, 
                      and they do contain
                      xenon but these are a kind of metal halide lamp.  xenon 
                      is an active
                      ingredient used to produce some usable white light until 
                      the bulb warms up
                      enough for other active ingredients to evaporate.
                      More info on automotive headlight HID bulbs is in my 
                      Automotive Xenon Metal
                      Halide Page.
                      More info on xenon lamps is in:
                      my Short Arc Lamp Page.
                      my page on making xenon glow continuously.
                      my xenon top page,mostly on xenon strobes and flash units.
----------------------------------------------------------------------------

Blue LED Lamps!       in urban areas at night, blue lights have a tendency to
                      stand out.  for police emergency phones 
                      of blue lights was a result of "blue impact"  or 
                      stimulation of blue-sensing light sensors in human eyes.
                      Back when lumen was defined in terms of 
                      photopic function (1931 CIE "Y-bar" function), blumens 
                      equals lumens times ratio z to y chromaticity coordinates
                      1988 redefinition of photopic function messes this up, 
                      LED blue lights for police emergency phones. Most have 
                      usual 470  nm blue LEDs.
                      current bright blue LEDs around 466-470 nm. 
                      blue peak of human vision is a little
                      below 450 nm. 
----------------------------------------------------------------------------

Incandescent_History  of  Bulbs
                      Thomas Alvin Edison invented first practical i
                      incandescent lamp, using a carbon filament in a bulb
                      containing a vacuum. Since that time, incandescent 
                      using tantalum and later tungsten filaments, 
                      which evaporate more slowly than carbon.
                      Nowadays, incandescent lamps  still made with tungsten 
                      filament's temperature is  generally over 2000 degrees
                      Celsius, or generally over 3600 degrees Fahrenheit. In a 
                      "standard" 75 or 100 watt 120 volt bulb, 
                      temperature is roughly 2550 degrees
                      Celsius, or roughly 4600 degrees Fahrenheit.
                      100 watt "standard" bulb  rated light 
                      efficiency is 17.5 lumens per watt.  
                      "ideal" 242.5 lumens per watt for idealized  white light,
                      or 681 lumens per watt ideally for yellowish-green 
                      wavelength of light thathuman eye is most sensitive to.
                      Most bulbs 8 to 21 lumens per watt 
                      tungsten filaments radiate mostly infrared radiation 
                      at any temperature that they can withstand. 
                      ideal thermal radiator produces visible 
                      light most efficiently at temperatures 
                      around 6300 Celsius (6600 Kelvin or 11,500 degrees
                      Fahrenheit). Even at this high temperature,
                      lot of radiation is either infrared or ultraviolet,
                      and theoretical luminous efficiency is 95lumens per watt.
                      Of course, nothing known to any humans is solid and usable
                      surface of the sun is not quite that hot.
                      efficiency of an incandescent bulb can be
                      increased by increasing the filament temperature,
                      which makes it burn outmore quickly.
                      At first, incandescent bulbs were made with  vacuum 
                      Later, inert gas such as argon or an argon-nitrogen
                      mixture slows down evaporation of filament. 
                      Tungsten atoms evaporating from  filament 
                      can be bounced back to the filament by gas atoms. 
                      a fill gas conducts heat away from filament. 
                      conducted heat is lost, or wasted. 
                      amount of heat conducted is roughly proportional to
                      filament's length, but  not  with the diameter.
                      bulbs with thin filaments and lower currents are
                      more efficient with a vacuum, 
                      higher current bulbs with thicker
                      filaments are more efficient with a fill gas.  
                      break-even point around 6-10 watts/cm of filament.
                      break-even point may be higher in larger bulbs 
                      where convection may increase heat removal from 
                      filament by the gas.
                      Sometimes, premium gases such as krypton or xenon  use 
                      These gases have larger atoms 
                      better at bouncing evaporated tungsten atoms back
                      to filament. also conduct heat less than argon. 
                      xenon is better, but more expensive. Either of will
                      improve life of the bulb, or in efficiency, or both.
                      How light bulbs burn out
                      high temperature that a tungsten filament is at, some of
                      tungsten evaporates during use. 
                      filament does not evaporate evenly.
                      These thin spots cause problems. 
                      resistance is greater than
                      more heat is generated where filament is thinner.
                      thin parts also have less surface area to radiate heat 
                      "double whammy" causes thin spots evaporate more quickly.
                      at increasing speed until a thin part of  filament 
                      either melts or becomes weak and breaks.
                      Why bulbs often burn out when you turn them on
                      urban folklore.
                      filament warms up very rapidly.  energy consumed
                      to warm up a cold filament is less than it would consume 
                      in one second of normal operation.
                      Long-life bulbs a slightly lower filament
                      temperature than usual. 
                      an ordinary silicon diode built into a cap
                      made to stick to base of a light bulb.
                      current through in only one direction, 
                      effectively reduces applied voltage by about 30 percent.
                      life expectancy is increased very dramatically. 
                      power consumption is reduced by about 40 percent
                      light output is reduced by reduced 
                      by about 70 percent (cooler filaments 
                      are less efficient at radiating visible light).
                      Soft-start devices
                      Since bulbs usually burn out during current surge
                      available in form built into caps one could stick onto 
                      tip of base of a light bulb. 
                      These devices are "negative temperature
                      coefficient thermistors", having a resistance that
                      decrease when they heat up.
                      When  bulb is first started, thermistor is cool and 
                      has a moderately high resistance 
                      this extends the life of bulbs less than one might think. 
                      DC vs. AC operation
                      As tungsten atoms evaporate from the filament, a very 
                      small percentage of are ionized by small amounts 
                      of short-wave ultraviolet light radiated by  filament, 
                      electric field around filament, or by free
                      electrons that escape from the filament by thermionic 
                      emission. tungsten ions are positively charged, 
                      and tend to leave positive end of filament 
                      and are attracted to the negative end of filament. 
                      result is that light bulbs operated on DC have this 
                      specific mechanism that
                      would cause uneven filament evaporation.
                      mechanism is generally not significant, 
                      fluorescent, compact fluorescent, 
                      or HID (mercury, metal halide, or sodium) lamps since
                      3 to 5 times as efficient as incandescent lamps.
----------------------------------------------------------------------------

Halogen Bulbs         halogen cycle,  halogen bulb is incandescent bulb, 
                      fill gas includes traces of a halogen, often but not 
                      necessarily iodine to return evaporated tungsten to 
                      filament.
                      As tungsten evaporates from filament, it usually 
                      condenses on the inner surface of the bulb. 
                      halogen is chemically reactive, and combines with
                      this tungsten deposit on glass to produce tungsten 
                      halides, which evaporate fairly easily. 
                      When tungsten halide reaches filament, 
                      intense heat of filament causes  halide to break 
                      down, releasing tungsten back to  filament.
                      known as the halogen cycle, extends life of filament
                      uneven filament evaporation and uneven deposition of
                      do occur, which limits halogen cycle to prolong life 
                      of bulb. However,halogen cycle 
                      keeps inner surface of bulb clean. 
                      lets halogen bulbs stay close to full brightness as age.
                      for halogen cycle to work, bulb surface generally 
                      over 250 degrees Celsius (482 degrees Fahrenheit). 
                      halogen maynot adequately vaporize or fail to react with 
                      condensed tungsten if bulb is too cool. 
                      means that the bulb must be small and made of
                      either quartz or a high-strength, heat-resistant grade of 
                      glass known as  "hard glass".
                      Since bulb is small and usually fairly strong,  
                      bulb filled with gas to a higher pressure than usual. 
                      This slows down evaporation of filament.
                      higher pressure and better fill gases can extend life
                      of bulb and/or permit a higher filament temperature 
                      that results in higher efficiency.
                      premium fill gases also results in less heat
                      being conducted from  filament by fill gas
                      halogen bulb is often 10 to 20 percent more efficient 
                      than an ordinary incandescent bulb 
                      also have two to three times  lifetime as ordinary bulbs,
                      Halogen bulbs fail same way ordinary incandescent bulbs
                      melting or breakage of a thin spot in an aging filament.
                      However,are additional failure modes.
                      filament notching or necking. Since  ends of 
                      filament are somewhat cool where  filament
                      is attached to  lead wires,
                      halogen attacks filament at these points. 
                      thin spots get hotter, which stops erosion 
                      at these points. However, parts of  filament even
                      closer to endpoints remain cool and continued erosion.
                      not so bad during continuous operation, thin spots do not
                      overheat. If  continues long enough, thin spots can become
                      weak enough to break from weight of  filament.
                      One major problem with the "necked" ends of the filament 
                      "necks" can overheat and melt or break
                      when the bulb is turned on. "soft-start" device
                      prevents overheating of "necks",
                      improving the bulb's ability to survive "necking". 
----------------------------------------------------------------------------

Carbon arc basics:    carbon arc predating  invention of incandescent lamp
                      Until advent of high intensity gas discharge lamps, 
                      motion picture projectors in movie theaters 
                      used carbon arc lamps. 
                      Sometimes rods would need to be changed 
                      in middle of reel and screen would go dark 
                      pair of carbon rod electrodes are
                      connected to a current limited source of power - 115 V AC 
                      or DC in series with a 1500 W space heater, 
                      mounted on fire proof structure which allows distance 
                      between  rods to be controlled.
                      Carbon rods can be extracted from most flashlight 
                      batteries, preferably c-cells for currents 
                      around 10-15 amps or so. cheapest types of batteries 
                      such as Radio Shack's 
                      have carbon rods, only slightly corrosive gunk. 
                      gunk must be cleaned off  carbon rods, anything else
                      this stuff is manganese dioxide, can corrode some metals
                      when wet, may increase  flammability of a few substances
                      get it onanything washable,
                      can be removed diluted sulfuric or hydrochloric acid.
                      Remove traces of acid with  baking soda.
                      Carbon rods made for carbon arcs are available at some 
                      welding supply stores. 
                      These carbon rods often have a copper jacket to 
                      improve conductivity. 
                      copper melts away from the tips of  carbon rods,
                      exposing a short portion of the carbon rod.
                      Do not connect an arc directly to a power source. 
                      Something must be in
                      series with it to limit current. Most arcs have a slightly 
                      nasty
                      characteristic, becoming greatly more conductive as they 
                      get hotter. Without
                      current limiting, an arc will draw current largely limited 
                      by your household
                      wiring, and might even cause nasty effects of many kinds 
                      before your fuse
                      blows/breaker pops.
                      For a do-it-yourself carbon arc, current limiting is 
                      usually done with some
                      sort of high-wattage heating device such as a space 
                      heater. This is used as
                      a resistor.
                      To start the arc, the power is turned on with the carbon 
                      rods separated.
                      They are then brought together until they touch and 
                      gradually separated
                      until a nice steady (and extremely bright!) arc is formed.
                      The carbon arc itself is fairly bright, but the tips of 
                      the carbon rods are
                      usually much brighter. The tips of the carbon rods get 
                      heated up to a
                      temperature usually near 3600 degrees Celsius, or approx. 
                      6500 degrees
                      Fahrenheit. This is near the melting point of carbon. At 
                      this temperature,
                      the carbon tips are brighter than halogen lamp filaments 
                      of comparable size.
                      If you heat the carbon rod tips to the melting point of 
                      carbon, you will
                      probably *not* get puddles or even dripping drops of 
                      molten carbon, since
                      molten carbon evaporates VERY easily.
                      In addition to light, there is usually generation of 
                      noxious smoke, carbon
                      dioxide, possibly significant amounts of carbon monoxide, 
                      oxides of
                      nitrogen, - and possibly small quantities of Bucky-Balls
                      (Buckmisterfullerine, C60) as well.
                      Although the carbon monoxide emissions are usually 
                      minimal, they could be
                      much greater if the arc is enclosed in a partially closed 
                      container that
                      lets just the wrong amount of oxygen interact with the hot 
                      carbon and/or
                      carbon vapor. Because of the possibility of carbon 
                      monoxide as well as other
                      noxious gases and fumes, it is recommended not to operate 
                      a carbon arc
                      indoors for more than a few seconds unless ventillation is 
                      very good.
                      The light emission is broad spectrum including IR and UV 
                      (often in hazardous
                      quantities if not filtered). The UV content contains 
                      significant UV-B and
                      some UV-C (shortwave UV) which is hazardous to skin and 
                      eyes. Ordinary glass
                      stops these, but plenty of UV-A (longwave UV) gets through 
                      glass, and this
                      may be hazardous to eyes at high intensities.
                      Please note that the white-hot carbon rod tips are 
                      hazardous to look at,
                      even if all UV and IR is removed. They are several times 
                      brighter than a
                      halogen lamp filament of similar size. If you use goggles 
                      made for acetylene
                      welding, then you can probably safely look at a carbon arc 
                      for a few
                      seconds. These give some light attenuation, along with 
                      greater attenuation
                      of UV and IR. To safely look at such arcs for prolonged 
                      periods of time, an
                      appropriate arc-welding face mask is recommended. 
                      Acetylene goggles let
                      through too much light and possibly too much UV to stare 
                      at the arc for much
                      more than several seconds. You also need to protect all 
                      exposed skin from
                      shortwave and mediumwave UV if you will encounter more 
                      than casual exposure
                      to arc radiation.
                      As the the carbon electrodes wear, they must be moved to 
                      maintain the
                      distance between them constant. Actual carbon arc 
                      equipment used a feedback
                      mechanism which monitored the current and adjusted rod 
                      position to keep it
                      constant (the current would decrease as the arc length 
                      increased). The light
                      output from such devices was remarkably constant.
                      DC Carbon Arcs
                      Arcs are not electrically symmetric. If an arc is powered 
                      by DC, one end is
                      usually different from the other. In DC welding arcs, the 
                      greatest
                      concentration of heat usually occurs at the negative end 
                      due to the "cathode
                      fall", the voltage drop involved in getting electrons from 
                      metal into the
                      gas or vapor. In addition, since some of the metal vapor 
                      is in the form of
                      positive ions, metal tends to be depleted from the 
                      positive electrode and
                      some of this may even be deposited on the negative 
                      electrode.
                      DC carbon arcs are similarly assymetric. The positive 
                      electrode is depleted
                      more rapidly than the negative one. A crater usually forms 
                      in the tip of the
                      positive electrode.
                      Unlike most arcs involving metals, the cathode fall in a 
                      decent carbon arc
                      seems to be minimal. The positive electrode makes more 
                      light than the
                      negative one in most cases. In carbon arc searchlights and 
                      projection
                      systems, a DC arc is usually used so that most of the 
                      light is emitted from
                      only one spot, the crater in the tip of the positive 
                      electrode.
                      If you find the negative electrode to be as bright as the 
                      positive one or
                      brighter, you may have too little current for the size of 
                      your carbon rods.
                      You may want thinner carbon rods, or more likely, more 
                      current. Low current
                      reduces cathode heating, which makes electron emission 
                      more difficult. This
                      increases the cathode fall, which results in cathode 
                      heating nearly as great
                      as that of higher currents.
                      Carbon arcs for fun and danger:
                      Note: these sorts of experiments are particularly 
                      hazardous - duplicate at
                      your own risk. There is danger from AC line connected high 
                      power, risk of
                      setting fire to something including yourself, and risk 
                      from substantial
                      emission of shortwave and mediumwave UV which is bad for 
                      skin and eyes, and
                      the risk of noxious fumes and/or gases.
                      --------------------------------------------------
                      (From: Arnold Pomerance (pomeranc@goldsword.com)).
                      Here is some information about carbon arcs that may be 
                      helpful to your
                      story.
                      Back in junior high school (1962) I built a small open-top 
                      carbon arc
                      furnace as a science project whose topic was "How are 
                      metals melted?". It
                      attracted a lot of attention at the school science fair, 
                      since it produced a
                      *lot* more light than heat! :)
                      I recently came across parts of it while cleaning out my 
                      parents' house.
                      Looking back on that project, it was incredibly dangerous, 
                      and I am very
                      lucky not to have been injured.
                      Anyway, I managed to drill two 1/2 inch holes across from 
                      each other, about
                      halfway up the sides of an ordinary clay flower pot whose 
                      top was about 6
                      inches in diameter. With black furnace cement I glued its 
                      base to a piece of
                      firebrick for stability. The firebrick was held loosely 
                      captive by four
                      small wooden blocks screwed onto a piece of plywood about 
                      two feet square.
                      On both sides of it I mounted some vertical 2 by 4 wood 
                      uprights, with 1/2
                      inch holes drilled in them that were lined up with the 
                      holes in the flower
                      pot. The uprights were about 6 inches out from the pot on 
                      each side.
                      For electrode holders I used foot-long pieces of 3/8 inch 
                      (outside diameter)
                      copper tubing. For safety (ha!) I press fitted them 
                      tightly into lengthwise
                      3/8 inch holes drilled about 2 inches deep in 4 inch 
                      pieces of wooden dowels
                      (i.e., cut up broomstick handle), to act as protective 
                      handles. Well, they
                      were protective in the sense of being relatively 
                      nonconductive for both heat
                      and electricity! :) These electrode holders could be slid 
                      towards and away
                      from each other, to meet in the center of the flower pot.
                      Power entered a small pull-handle fuse box (also mounted 
                      on the plywood,
                      near the front) via a 120V 15A cord which could be plugged 
                      into any
                      convenient outlet. From the fuse box, I connected one side 
                      to my parents'
                      portable broiler (i.e., using it as a high-wattage 10A 
                      ballast resistor)
                      which sat behind everything else, out of the way. I 
                      connected the other side
                      of the broiler to one of the electrode holders. I 
                      completed the circuit by
                      connecting from the other electrode holder back to the 
                      fuse box.
                      The wiring was flexible high-temperature cord, such as for 
                      a steam iron,
                      with both conductors twisted together at both ends to 
                      double its current
                      carrying capacity (and because I only needed one 
                      conductor) on each leg. I
                      stripped about 1.5 inches of the stranded copper wire and 
                      fastened it to the
                      copper tubing by looping it around the tubing and snugging 
                      it up to itself
                      with an ordinary split-bolt lug. (Yes, it needed to be 
                      re-snugged every once
                      in a while; I never did figure out a better way at the 
                      time; I suppose
                      nowadays I would use a screw into the tubing...) At the 
                      broiler, I simply
                      wrapped the copper strands around the pins that normally 
                      would accept the
                      socket end of an appliance cord. :)
                      I was *very* aware of all the exposed 120V connections! 
                      The pull handle on
                      the little fuse box was a very reassuring safety device, 
                      and I never
                      hesitated to pull it to disconnect the power whenever 
                      anything needed to be
                      adjusted, or connections tightened, or electrodes changed, 
                      or experiments
                      set up...
                      Finding a supply of solid carbon electrodes was no 
                      problem: I merely
                      hacksawed open some used D cell batteries and pulled their 
                      carbon rods out!
                      Then of course I had to scrape all that yucky acid gunk 
                      off them with a
                      pocket knife! :-o But they were conveniently about 1/4 
                      inch in diameter, and
                      could be pressed (with difficulty) into the copper tubing, 
                      whose ends had
                      been flared somewhat with a screwdriver.
                      When setting up the furnace, I would scoop about an inch 
                      or two of
                      vermiculite granules into the bottom of the flower pot as 
                      a heat resistant
                      blanket to catch any hot objects (including loose carbon 
                      rods!) that might
                      fall from the arc region.
                      To operate: Separate the carbons about a half inch. Turn 
                      on the power. Put
                      on a welding hood. (Actually, I used ordinary sunglasses, 
                      and suffered
                      ultraviolet burns of the eyes as a result of inadequate 
                      protection; for
                      several days afterwards my eyes felt as if they had gravel 
                      in them!) :( Move
                      the electrodes towards each other until they touch. Loud 
                      hummmm! Slowly pull
                      them apart about 1/4 inch to create the arc. Tremendous 
                      blue-white light!
                      Loud, raspy buzzing at about 120 Hz! Steady wisps of burnt 
                      carbon-smelling
                      smoke! (Mostly from vaporizing carbon, but for the first 
                      few minutes from
                      remnants of the battery chemicals also.) 8-o
                      If left alone, the arc was stable for only a minute or 
                      two, because the
                      carbons gradually eroded, making the arc longer and longer 
                      until it was too
                      long to sustain itself. So I had to gently adjust the 
                      spacing frequently. I
                      remember noting that a long arc was considerably brighter 
                      and noisier than a
                      short arc, so I could sort of tell what the spacing was 
                      without looking at
                      it. As if there were any way I *COULD* look at it--my 
                      measurement technique
                      consisted of killing the power and then looking! :)
                      For my experiments I cut small tin cans into winged shapes 
                      to make little
                      pots (crucibles, kind of) for melting things like lead 
                      tire weights and
                      other metal scraps, suspended about an inch over the arc 
                      by hanging (with
                      their wings) from the top of the flower pot. Water in such 
                      a pot would boil
                      in a minute or so. Of course the steel pots would oxidize 
                      and eventually
                      burn through. To demonstrate melting a scrap of solid 
                      copper wire I had to
                      forego using a pot and instead pass the wire directly 
                      through the center of
                      the arc while holding it with long nose pliers (and 
                      wearing thick gloves!)
                      :-o
                      Years later I read that carbon arcs tend to produce large 
                      quantities of
                      carbon monoxide gas, so professional carbon arc lights 
                      have vent pipes to
                      carry it away. :( I hadn't known that, or even guessed. 
                      Like I say, I was
                      lucky!
                      I also read that professional carbon arc lights use DC 
                      instead of AC for
                      several reasons: A DC arc is continuous and reliable, 
                      whereas an AC arc must
                      re-strike itself many times each second and tends to blow 
                      out more often.
                      There is less buzzing with DC than with AC. With DC, there 
                      is just one spot
                      of bright light (anode? cathode?) to focus with the 
                      lenses, instead of two
                      spots. (Apparently the electrode tip is a much brighter 
                      source of light than
                      the arc itself.)
                      On the other hand, one of the DC electrodes will erode 
                      considerably faster
                      than the other, as opposed to equal erosion with AC. Also, 
                      a DC arc requires
                      a steady (preferably regulated) source of DC, whereas an 
                      AC arc can get by
                      with just a ballast resistor. Sorry, I never measured the 
                      current or
                      voltage, so I don't know what the effective resistance of 
                      my arc was.
                      ---------------------------------------------------------------------
                      Brighter Illuminating Arcs
                      1) Cored Carbons
                      The arc can be enhanced by using hollow rods that are 
                      stuffed with other
                      substances whose vapors glow brightly in arcs. Various 
                      metal salts are
                      usually used for this. Ordinary sodium chloride even works 
                      for this,
                      resulting in large quantities of orange-yellow light. 
                      Strontium compounds
                      will produce a more red or pink color.
                      Please note that the salt vapors will condense into smoky 
                      fumes when they
                      leave the arc. Depending on the substance used, these 
                      fumes may be hazardous
                      to breathe and/or cause corrosion problems if they settle 
                      on metal parts,
                      especially if combined with moisture or even humidity 
                      afterwards.
                      2) Magnetite Arc
                      Sometime way back when the high-pressure mercury lamp was 
                      not yet used for
                      street lighting, arc lamps were used in a few locations 
                      for this purpose.
                      Charles Steinmetz was able to improve on the carbon arc by 
                      using magnetite
                      (an iron ore mineral) instead of carbon. The magnetite 
                      released iron vapor
                      into the arc. Like many other metal vapors, iron vapor 
                      results in a
                      brilliant arc with a characteristic color. Iron arcs are 
                      typically a
                      purplish shade of blue-white.
                      Please read Don Klipstein's Disclaimers.
                      --end V. 1.03 (carbon arcs)
                      Some arc metal melting experiments by Klaas ("C++ freak").
                      (Ditzhuyzen.Klaas.van@uniface.nl) Caution, such 
                      experimentation can be
                      hazardous.
                      A bit of carbon arc lamp history including a few details 
                      and some photos of
                      actual historic arc lamps. (from the Insitiute of 
                      Electrical Engineers in
                      the UK)
                      Compact Fluorescent Lamps
----------------------------------------------------------------------------


compact fluorescent   lamp?
                      compact fluorescent lamp is actually a fairly 
                      conventional, although
                      somewhat miniaturized fluorescent tube packaged with an 
                      integral ballast
                      (either iron ("magnetic") or electronic) in a standard 
                      crew base that can
                      be installed into nearly any table lamp or lighting 
                      fixture.
                      Some compact fluorescents are of the "modular" type, 
                      having bulbs and
                      ballasts that can be separated and replaced separately.  
                      Others are of the
                      "integral" type, in which the ballast is permanently built 
                      into the bulb
                      and is discarded with the bulb when the bulb burns out.
                      These types are being heavily promoted as energy savings 
                      alternatives
                      to incandescent lamps.  They also have a much longer life 
                      - usually
                      7500-10,000 hours, sometimes up to 20,000 hours compared 
                      to 750 to 1000
                      hours for a standard incandescent.  While these basic 
                      premises are not in
                      dispute - all is not peaches and cream:
                      1.  They are often physically larger than the incandescent 
                      bulbs they replace
                          and simply may not fit the lamp or fixture 
                      conveniently or at all.
                      2.  The funny elongated or circular shape may result in a 
                      less optimal
                          lighting pattern.
                      3.  Many models have light output claims that are only 
                      achieved at the
                          optimum operating temperature and/or in some optimum 
                      burning position
                          that achieves an optimum internal temperature.  Many 
                      light output
                          claims are outright exaggerated, often by about 15 
                      percent and in a
                          few extreme cases by 25 percent.
                      4.  Compact fluorescent lamps usually do not produce full 
                      light output
                          until they warm up for a minute or two.  A few models 
                      require about
                          three minutes to fully warm up and produce as little 
                      as 20-25 percent
                          of their full light output when first started.
                      5.  The light is usually slightly different from that of 
                      incandescents,
                          often slightly less yellow and slightly more pink, 
                      more purple, or
                          more blue. The spectral output of these lamps is 
                      usually concentrated
                          in a few specific bands of the spectrum, and this can 
                      slightly distort
                          color rendering.
                          Any color difference from other nearby lamps may be 
                      undesirable and
                          result in less than pleasing contrast with ordinary 
                      lamps and ceiling
                          fixtures.  Newer models have been addressing this 
                      issue.
                      6.  Some types (usually iron ballasts) may produce an 
                      annoying 120 Hz
                          (or 100 Hz) flicker.
                      7.  Ordinary dimmers cannot be used with compact 
                      fluorescents.
                      8.  Like other fluorescents, operation at cold 
                      temperatures (under around
                          50 degrees F) may cause reduced light output or 
                      erratic operation.
                          Some models work fairly well down to about 35 degrees 
                      F, others may
                          get noticeably dim below 60 degrees F.  The optimum 
                      temperature range
                          of a particular lamp may vary with burning position, 
                      generally
                          preferring cooler temperatures if operated base-down.
                          Compact fluorescents may also not like excessive heat.  
                      Some ballasts
                          are unreliable in ambient temperatures much over 120 
                      degrees F.  This
                          is sometimes a problem in enclosed or recessed ceiling 
                      fixtures if
                          heat in the fixture builds up.
                      9.  There may be am audible buzz from the ballast, usually 
                      from iron
                          ballasts.
                      10.  They may produce Radio Frequency Interference (RFI).
                      11.  The up-front cost is substantial (unless there is a 
                      large rebate): $10
                          to $20 for a compact fluorescent to replace a 60 W 
                      incandescent bulb!
                      12. Due to the high up-front cost, the pay-back period may 
                      approach infinity.
                      13. While their life may be 20,000 hours, a wayward 
                      baseball will break
                          one of these $10 to $20 bulbs as easily as a 25 cent 
                      incandescent.
                      14. Few commonly available compact fluorescent lamps 
                      designed to fit
                          into 120 volt ordinary light bulb sockets match or 
                      exceed the
                          light output of a 100 watt standard incandescent lamp.  
                      One not-so-
                          compact "circline" unit designed to fit into table 
                      lamps is about as
                          bright as a 100 watt bulb, or slightly brighter, but 
                      is claimed
                          to be as bright as a 150 watt bulb.
                          A 28 watt General Electric model matches "100 watt" 
                      brightness, but
                          has above-average RFI emissions.  Lights of America 
                      produces a 34 watt
                          model that slightly outshines a 100 watt lightbulb and 
                      a 45 watt model
                          that is almost as bright as a 150 watt lightbulb.  
                      Beware of higher
                          claims on the packages that are met only in specific 
                      (probably
                          unusual) conditions - if at all.
                      15. Like other fluorescent lamps, compact fluorescent 
                      amps should only
                          be used where they are left on (on an average) at 
                      least 15 minutes,
                          preferably at least a half hour, once they are turned 
                      on.  Starting
                          a fluorescent lamp causes wear and tear on the 
                      electrodes (except for
                          a few specific exceptions such as RF electrodeless 
                      lamps).
                      Nonetheless, due to the lower energy use and cooler 
                      operation, compact
                      fluorescents do represent a desirable alternative to 
                      incandescents.  Just
                      don't open that investment account for all your increased 
                      savings just yet!
                        -- end V. 1.10 --
                      Here are a few specific recommendations as to lamp types
                      tested/studied/reviewed by Donald L. Klipstein.
                      ePanorama.net - Electronic components
                        ------------------------------------------------------------------------

Gas discharge lamp    basics
                      Neon signs are powered by transformers or electronic 
                      ballasts
                      producing up to 15,000 V or more. only safe way 
                      to work is to assume are potentially lethal and treat 
                      them with respect.
                      Hazards include:
                      Electric shock. There is usually little need to probe 
                      a live fixture.
                      Most problems can be identified by inspection or with 
                      an ohmmeter or continuity tester when unplugged.
                      Discharge lamps and fixtures using iron ballasts 
                      are basically pretty inert when unplugged. 
                      Even if there are small capacitors inside  ballast(s) 
                      or for RFI prevention, these are not likely
                      to bite.
                      Nasty chemicals: (sodium and mercury) and 
                      Ultra-Violet (UV) light: High intensity discharge 
                      nasty UV-B variety.
                      short wave radiation will be blocked by the outer
                      glass envelope and/or phosphor coating. However, 
                      should the outer envelope break or be removed, 
                      lamp will still operate (at least for
                      a while - some have a means of disabling themselves 
                      after a few hours
                      or less of exposure to air). DO NOT operate such a 
                      lamp preferably at
                      all but if you do, at least take appropriate 
                      precautions to avoid any
                      exposure to the UV radiation.
----------------------------------------------------------------------------

Neon tubes            have electrodes sealed in at each end. 
                      formed using the glass blower's skill in the shape of 
                      letters,Black paint is used to block off areas  dark.  are
                      evacuated, backfilled, heated (bombarded - usually by a 
                      discharge through tube at a very high current) 
                      to drive off any impurities, evacuated and
                      then backfilled with a variety of low pressure gasses.
                      Neon is the most widely known with its characteristic 
                      red-orange glow. Neon
                      may be combined with an internal phosphor coating (like a 
                      fluorescent tube)
                      to utilize neon's weak short-wave UV emissions. A 
                      green-emitting phosphor
                      combines with neon's red-orange glow to make a less-red 
                      shade of orange. 
                      blue-emitting phosphor may be used to result in a hot-pink
                      color. Neon may
                      be used in tubing made of red glass to produce a deep red 
                      color.
                      Other colors are usually produced by tubing containing 
                      argon and mercury
                      vapor. The mercury is the active ingredient, the argon 
                      produces negligible
                      radiation of any kind but is important for the "neon" 
                      tubing to work. Clear
                      tubing with mercury/argon glows a characteristic light 
                      blue color.
                      Such tubing is often phosphor-coated on the inside, to 
                      utilize the major
                      short-wave UV emission of low-pressure mercury. In this 
                      way, much of the
                      "neon" tubes in use are a kind of fluorescent lamp.
                      Phosphor-coated tubing with mercury can glow blue, 
                      blue-green, slightly
                      white-ish green, light yellow, bright pink, light purple, 
                      or white.
                      Use of mercury vapor with colored tubing (with or without 
                      phosphors) can
                      provide a lime-green or deep blue or deep violet-blue.
                      Nowadays, nearly all "neon" tubing contains neon or 
                      mercury vapor (with
                      argon), whether with or without phosphors and/or colored 
                      glass. Well in the
                      past, various colors were obtained (generally at reduced 
                      efficiency) by
                      using different gases.
                      For example, helium can produce a white-ish orange light 
                      in shorter length,
                      smaller diameter tubing. Hydrogen in this case makes a 
                      lavender-hot-pink
                      color. These gases glow more dimly with duller color 
                      shades in larger
                      tubing. Krypton makes a dull greenish color.Argon makes a 
                      dimmish purple
                      color. Nitrogen (generally in shorter length tubing) makes
                      a grayish
                      purple-pink color. Xenon, which is expensive, generally 
                      glows with a dim
                      bluish gray color, along with the glass tubing giving a 
                      slight dim blue
                      fluorescence from very short wave UV from the xenon 
                      discharge. Krypton also
                      often causes a dim blue glass fluorescence.
----------------------------------------------------------------------------

Power Supplies        for Neon
                      output is typically 6,000 to 15,000 VAC at 15 to 60 mA. 
                      One such unit can power 10s of feet of tubing. 
                      This transformer acts as its own ballast 
                      providing the high voltage needed for starting 
                      and limiting the running current as well.
                      Warning: output of these transformers can be lethal 
                      since even limited current  is relatively high.
                      newest neon sign power supplies use an
                      electronic AC-AC inverter greatly reducing size and 
                      weight  by eliminating large heavy iron transformer.
                      Small neon lamps inside high-tech phones and such also use
                      solid state inverters to provide
                      more modest voltage required for these devices.
----------------------------------------------------------------------------

Neon Sign             Installation
                      (From: Clive Mitchell (clive@emanator.co.uk)).
                      voltage required to light a run of neon tube is 
                      variable according to diameter, gas type, pressure 
                      and number of tubes in circuit.
                      For a 15 kV transformer and neon gas you could run:
                      * 33 feet  of 10 mm tube,
                      * 45 feet  of 12 mm tube,
                      * 60 feet  of 15 mm tube,
                      * 78 feet  of 20 mm tube,
                      * 102 feet of 25 mm tube.
                      * Deduct one foot of tube for every pair of electrodes 
                      (tube section).
                      based on a chart in "Neon Techniques And Handling" which
                      is  traditional neon reference.
                      larger the diameter of the tube, lower voltage required, 
                      and dimmer it will be. Transformers come with different 
                      current ratings. For
                      larger diameter tubes, you can increase brightness by 
                      using a highercurrent.
                      * Don't attempt to run too much tube on a transformer, 
                      since it can cause
                      breakdown of the insulation and destroy  transformer.
                      * Don't attempt to run too little tube on a 
                      transformer, since it cancause overheating and burn-out.
                      It is absolutely imperative that proper neon sign cabling 
                      and insulators are
                      used, and that all local regulations are strictly 
                      followed. If you are
                      intending to work with neon tubing, you should learn as 
                      much as possible
                      neon poses  shock and  fire risk if installed incorrectly
----------------------------------------------------------------------------

neon circuit          is not so simple. 
                      In a standard AC circuit neon acts like a diac
                      high breakover voltage followed by fast drop resistance.
                      Neon sign transformers are designed to 'leak' 
                      and thus  self-regulate. You have a
                      combined resistive and reactive circuit.
                      But take heart, it's all been figured out. :-)
                      'purely' neon filled tube has a higher
                      voltage requirement than an argon-mercury tube 
                      voltage  varies inversely with tubing diameter. That
                      is large diameters of a lower voltage requirement 
                      than small diameters.
                      voltage requirement varies directly with tubing length.
                      number of units (or pairs of electrodes) 
                      increases the voltage
                      requirement because the electrodes have a voltage drop.
                      Wiring methods and length will also contribute to the 
                      formula but
----------------------------------------------------------------------------

HID                   High Intensity discharge Lamps
                      High Intensity Discharge (HID) Lamp Technology
                      used  in street, stadium, and factory
                      smaller sizes have become  available for home yard
                      and crime prevention applications.
                      require a warmup period.
----------------------------------------------------------------------------

mercury vapor lamps   High pressure mercury vapor lamps contain an internal 
                      arc tube made ofquartz enclosed in outer glass envelope. 
                      A small amount of metallic (liquid) mercury 
                      is sealed in an argon gas fill 
                      inside the quartz tube.
                      After warmup period, arc emits both visible and (UV)
                      High pressure mercury vapor lamps (no color correction)
                      produce a blue-white light 
                      Phosphors can be used to give color closer to natural 
                      (Without color correction, people look like cadavers).
                      Mercury vapor lamps longest life of this class of bulbs
                      10,000 to 24,000 hours.  first introduced in 1934 
----------------------------------------------------------------------------

Metal halide lamps    Metal halide lamps  constructed similar  to mercury vapor
                      lamps. However, in addition to  mercury and argon, 
                      various metal halides are included in  gas fill. 
                      most popular is  sodium iodide and scandium iodide. 
                      few versions of  have lithium iodide as well.
                      much less common version has sodium iodide,
                      thallium iodide, and indium iodide. 
                      these compounds increases  luminous efficiency 
                      and more pleasing color
                      metal halide arc does not emit much UV.
----------------------------------------------------------------------------

sodium vapor lamps    High pressure sodium vapor lamps 
                      contain an internal arc tube made of a
                      translucent ceramic material aluminum oxide known as
                      "polycrystalline alumina"). Glass and quartz cannot 
                      maintain structural strength up to 1300 degrees C) 
                      encountered here, and hot sodium chemically attacks
                      quartz and glass. Like other HID lamps, the arc tube 
                      is enclosed in an outer glass envelope.
                      A small amount of metallic (solid) sodium in
                      addition to mercury is sealed in a xenon gas fill 
                      inside the ceramic arc tube. 
                      Some versions use a neon-argon mixture instead
                      of xenon. Basic operation is otherwise similar to 
                      mercury or metal halide lamps. 
                      High pressure sodium vapor lamps produce an orange-white
                     light and have a luminous efficiency much higher than 
                      mercury or metalhalide lamps.
                      Since hot liquid sodium often eventually leaches 
                      sodium lamps have a surplus of sodium in them.
                      Proper lamp operation depends on the sodium reservoir 
                      being within a proper temperature range.
----------------------------------------------------------------------------

Mercury vapor lamps   are roughly as efficient as fluorescent lamps. Metal
                      halide lamps around 50 to 75 percent more efficient t
                      High pressure sodium lamps twice as efficient 
                      Unlike fluorescent lamps,HID lamps 
                      wide range of temperatures.
                      makes HID lamps more suitable than
                      fluorescent lamps for outdoor use.
                      When cold, the metallic mercury or sodium in arc tube 
                      is liquid or solid  at room temperature. 
                      During the starting process, a
                      low pressure discharge is established in gases. 
                      This produces very little light 
                      but heats metal contained inside the arc tube
                      and gradually vaporizes it. As this happens, 
                      pressure increases and light starts being produced 
                      by discharge through  high pressure metal vapor. 
                      light output  increases over period of a minute or more
                      entire warmup process may require up to 10 minutes,
                      typically takes 3 to 5  minutes. 
                      A hot lamp cannot be restarted until it has cooled 
                      since  voltage needed to restrike  arc is too high 
                      for the normal AC line/ballast  combination to provide.
                      Problems With High Intensity Discharge Lamps
                      HID lamps have a very long life compared to incandescents
                      (up to 24,000 hours), they do fail. 
                      ballasts can also go bad. 
                      light output falls off gradually as they age.
                      may drop to half original value towards end of  life.
                      lamp which is cycling - starting, warming up, then 
                      turning itself off - is
                      probably overheating due to a bad bulb or ballast. A 
                      thermal protector is probably shutting down fixture 
                      to protect it or arc is being extinguished on its own.
                      Warning: do not operate an HID lamp 
                      if outer glass envelope is cracked or broken. 
                      extremely hot arc tube can quite literally explode 
                      mercury arc produces substantial amounts of short wave UV 
                      outer glass normally blocks most 



                      own relatively quickly.
                      Troubleshooting a Discharge Lamp Fixture
                      (From: Greg Anderson (a3a30878@bc.sympatico.ca).)
                      The following applies directly to high pressure sodium 
                      lamps. It may also
                      also be used for metal halide and mercury vapour lamp 
                      problems as long as
                      references to the starter are ignored. (Metal halide and 
                      mercury vapour
                      lamps do not have starters, except for "instant re-light" 
                      metal hhalide
                      lamps.)
                      The starter produces about 2 to 5 kV spikes to ionize the 
                      gas in the lamp.
                      The starter normally has a triac across the ballast and a 
                      diac trigger cct.
                      When open cct voltage is across the lamp, the diac fires 
                      the triac to short
                      the ballast, the triac then opens. This "kick" produces 
                      the voltage spike.
                      Once the gas ionizes, the lamp impedance drops then 
                      gradually increases as
                      the lamp warms up. The lamp running voltage is about 1/2 
                      of the open cct
                      voltage
                      With the lamp removed and power on, you can normally hear 
                      a good starter
                      "ticking".
                      The open cct voltage is stamped on the ballast and is 
                      between about 150 and
                      350 Vac, depending on lamp wattage and ballast. Also, a 
                      capacitor is often
                      connected in series with lamp to improve peaking and 
                      ballast action.
                      Steps to follow:
                        1. Bypass the photo cell - It may be bad
                        2. Check connections - water, salt, and bird poop are 
                      not good for wiring
                        3. Check the capacitor, if installed - normally they 
                      blow-up when bad
                        4. Check for open/shorted ballast.
                        5. Power up and check for starter "ticking"
                        6. REMOVE starter from cct and measure open cct volts
                        7. Check/Replace lamp
                        8. Check/replace lamp socket
                        9. Replace starter
                       10. Replace complete fixture.
                       11. Replace electrician. :)
                      Repairing a starter is not economically viable and often 
                      proves that
                      electronic devices contain smoke and sometimes fire.
                      Ballasts and Bulbs Should be Matched!
                      HID bulbs generally need specific ballasts, and any given 
                      ballast can
                      usually safely and effectively operate only one type or a 
                      few types of HID
                      bulbs.
                      The bulb wattage must be matched to the ballast. A smaller 
                      bulb will usually
                      be fed a wattage close to what the proper bulb takes, and 
                      will generally
                      overheat and may catastrophically fail. Any catastrophic 
                      failures may not
                      necessarily happen quickly. A larger bulb will be 
                      underpowered, and will
                      operate at reduced efficiency and may have a shortened 
                      lifetime. The ballast
                      may also overheat from prolonged operation with an 
                      oversized bulb that fails
                      to warm up.
                      See The Discharge Lamp Mechanics Document (rather 
                      technical) for why it can
                      be bad to underpower an arc discharge lamp.
                      Even if the ballast and bulb wattages match, substitutions 
                      can be limited by
                      various factors including but not limited to different 
                      operating voltages
                      for different bulbs. Examples are:
                        1. Pulse-start sodium lamps often have a slightly lower 
                      operating voltage
                           than metal halide and mercury lamps of the same 
                      wattage, and ballasts
                           for these sodium bulbs provide slightly more current 
                      than mercury and
                           metal halide ballasts for the same wattage would. The 
                      higher current
                           provided by the pulse-start sodium ballast can 
                      overheat mercury and
                           metal halide lamps. Mercury and metal halide lamps 
                      may also "cycle" on
                           and off in lower voltage sodium ballasts, such as 
                      many 50 to 100 watt
                           ones.
                        2. Metal halide lamps have an operating voltage close to 
                      that of mercury
                           lamps in many wattages, but have stricter tolerances 
                      for wattage and
                           current waveform. Metal halides also usually need a 
                      higher starting
                           voltage. Most metal halide lamps 100 watts or smaller 
                      require a high
                           voltage starting pulse around or even over 1,000 
                      volts.
                           175 to 400 watt metal halide lamp ballasts can power 
                      mercury lamps of
                           the same wattage, but the reverse is not recommended. 
                      Mercury lamps 50
                           to 100 watts will work on metal halide ballasts, but 
                      hot restriking of
                           mercury lamps 100 watts or smaller on metal halide 
                      lamps may be hard on
                           the mercury lamp since the starting pulse can force 
                      current through
                           cold electrodes and the starting resistor inside the 
                      mercury lamp.
                        3. 1,000 watt mercury lamps come in two operating 
                      voltages, one of which
                           is OK for 1,000 watt metal halide ballasts. A few 
                      wattages of
                           pulse-start sodium (150 watts?) come in two voltages.
                           A low voltage lamp in a high voltage ballast will be 
                      underpowered,
                           resulting in reduced efficiency, possible reduced 
                      lamp life, and
                           possible ballast overheating. A high voltage lamp in 
                      a low voltage
                           ballast will usually cycle on and off, operate 
                      erratically, or possibly
                           overheat. This will usually result in greatly reduced 
                      lamp life in any
                           case.
                        4. One class of sodium lamps is made to work in mercury 
                      fixtures, but
                           these only work properly with some mercury ballasts, 
                      namely:
                              o 'Reactor' (plain inductor) ballasts on 230 to 
                      277 volt lines.
                              o 'High leakage reactance autotransformer' 
                      ballasts, preferably with
                                an open circuit voltage around 230 to 277 volts. 
                      NOT 'lead',
                                'lead-peak' nor any metal halide ballast!
                           These sodium lamps may suffer poor power regulation 
                      and accelerated
                           aging in the wrong mercury ballasts, especially after 
                      some normal aging
                           changes their electrical characteristics. Also, these 
                      lamps may
                           overheat and will probably have shortened life with 
                      pulse-start sodium
                           ballasts.
                        5. Many sodium lamps require a high voltage starting 
                      pulse provided only
                           by ballasts made to power such lamps.
                      Operation of Discharge Lamps on DC
                      Sometimes, one may want to run a discharge lamp on DC. 
                      There are two
                      possible reasons:
                         * Only DC power is available.
                         * To reduce flicker. Sometimes, the lamp performs 
                      differently for
                           electricity flowing in one direction than the other. 
                      In addition, the
                           positive and negative ends of the arc can make 
                      different amounts of
                           light, resulting in a flicker rate equal to the AC 
                      frequency rather
                           than twice the AC frequency.
                           However, end flicker is usually not significant. In 
                      HID lamps, the
                           total arc size is generally small. Only if the 
                      fixture has a reflector
                           that causes some areas to receive light from only one 
                      end of the arc
                           should end flicker be significant. In most multi-tube 
                      fluorescent
                           fixtures, the tubes are usually in series pairs with 
                      the two tubes in
                           any pair oriented in opposite directions. This 
                      generally reduces end
                           flicker effects, especially in fixtures with 
                      diffusing lenses.
                           Bulbs should perform close enough to identically in 
                      both directions,
                           unless the bulb is near the end of its life. In such 
                      a case, one
                           electrode deteriorates enough to affect performance 
                      before the other
                           does. However, this generally indicates a need to 
                      replace the bulb
                           rather than to attempt to make it flicker less.
                      If you want to rectify the AC to provide the bulb with DC, 
                      use a bridge
                      rectifier after the ballast. Most ballasts, including all 
                      "iron" types,
                      require AC of the proper voltage and frequency to work. Do 
                      this only if only
                      two wires feed the bulb. Otherwise, diodes in the bridge 
                      rectifier may short
                      parts of the ballast to each other, at least for half the 
                      AC cycle. Problems
                      can also occur with fluorescent ballasts with filament 
                      windings. Only fully
                      isolated filament windings or separate filament 
                      transformers should be used
                      if you rectify the output of a ballast with filament 
                      windings. Also, the
                      bridge rectifier must withstand the peak voltage provided 
                      by the ballast.
                      If the power supply is DC of adequate voltage, you need a 
                      resistor ballast
                      or an electronic ballast specifically designed to run your 
                      lamp from the
                      available DC voltage. "Iron" ballasts only limit current 
                      when used with AC.
                      Preheat fluorescent lamps operated from DC supplies and 
                      without special
                      ballasts need both the usual "iron" ballast to provide the 
                      starting "kick"
                      and a resistor to limit current.
                      In addition, most discharge lamps are only partially 
                      compatible with DC, and
                      some are not compatible at all.
                      Mercury vapor and fluorescent lamps generally work on DC. 
                      However, the life
                      may be shortened somewhat by uneven electrode wear.
                      Fluorescent lamps may get dim at one end with DC. Since 
                      the mercury vapor
                      ionizes more easily than the argon, some of it exists as 
                      positive ions. This
                      can cause the mercury to be pulled to the negative end of 
                      the tube,
                      resulting in a mercury shortage at the positive end. This 
                      is more of a
                      problem with longer length and smaller diameter tubes.
                      Some fluorescent fixtures made for use where the power 
                      available is DC have
                      special switches to reverse polarity every time the 
                      fixture is started. This
                      balances electrode wear and reduces mercury distribution 
                      problems.
                      Mercury vapor lamps generally work OK with DC, but some 
                      may only reliably
                      work properly if the tip of the base is negative and the 
                      shell of the base
                      is positive. This is because the starting electrode does 
                      its job best when
                      it is positive.
                      In addition, if the nearby main electrode is positive, it 
                      may cause a thin
                      film of metal condensation that shorts the starting 
                      electrode to the nearby
                      main electrode. This may make some brands, models, and 
                      sizes of mercury
                      lamps unable to start after some use. The negative main 
                      electrode will not
                      release as much vaporized electrode material, since the 
                      electrode material
                      easily forms positive ions making the electrode material 
                      vapor tend to
                      condense on the electrode rather than condense on nearby 
                      parts of the arc
                      tube.
                      Metal halide and sodium lamps should not get DC. Use these 
                      only with
                      ballasts that give the bulb AC. In metal halide lamps, 
                      ions from the molten
                      halide salts can leach into hot quartz in the presence of 
                      a DC electric
                      field. This can cause strains in the quartz arc tube. At 
                      the ends of the arc
                      tube, electrolysis may occur, releasing chemically 
                      reactive halide salt
                      components that can damage the arc tube or the electrodes. 
                      The arc tube may
                      crack as a result.
                      There are a few specialized metal halide lamps that are 
                      made to work on DC.
                      These often have asymmetrical electrodes and/or short arc 
                      lengths. These
                      lamps often also must be operated only in specific 
                      positions, and only with
                      the type of current they were designed for in order to 
                      achieve the proper
                      distribution of active ingredients within the arc tube and 
                      to achieve proper
                      electrode usage. For example, some of these lamps may go 
                      wrong in some way
                      or another with AC.
                      In high pressure sodium lamps, which contain both sodium 
                      and mercury, the
                      sodium forms positive ions more easily than the mercury 
                      does and drifts
                      towards the negative electrode. The positive end can go 
                      dim from a lack of
                      sodium. In addition, if any part of the arc tube is filled 
                      with a mixture
                      containing excessive sodium and a lack of mercury, heat 
                      conduction from that
                      part of the arc to the arc tube will increase. 
                      Furthermore, the hot arc tube
                      may suffer electrolysis problems over time in the presence 
                      of sodium ions
                      and a DC electric field.
                      Low pressure sodium lamps should not get DC for the same 
                      reasons. The sodium
                      is likely to drift to the negative end of the arc tube, 
                      and hot glass will
                      almost certainly experience destructive electrolysis 
                      problems if exposed to
                      hot sodium or sodium ions and a DC electric field.
                      Special purpose HID lamps such as xenon and HMI
                      The usual general purpose HID lamps are mercury vapor, 
                      metal halide, and
                      high pressure sodium. You can get these at home centers, 
                      although usually
                      only in wattages up to 400 watts. These versions of HID 
                      lamps are optimized
                      for high efficiency, long life, and minimized 
                      manufacturing cost.
                      However, the arc surface brightness of these lamps is 
                      roughly equal to the
                      surface brightness of incandescent lamp filaments and 
                      general purpose
                      halogen lamp filaments. For some applications such as 
                      endoscopy and movie
                      projection, it is necessary to have a much more 
                      concentrated light source.
                      This is where specialized HID lamps such as short arc 
                      lamps and HMI lamps
                      come in.
                      Short arc lamps consist of a roughly spherical quartz bulb 
                      with two heavy
                      duty electrodes spaced only a few millimeters apart at the 
                      tips. The bulb
                      may contain xenon or mercury or both. Mercury short arc 
                      lamps have an argon
                      gas fill for the arc to start in.
                      In a short arc lamp, the arc is small and extremely 
                      intense. The power input
                      is at least several hundred and more typically a few 
                      thousand watts per
                      centimeter of arc length. The operating pressure in the 
                      bulb is extremely
                      high - sometimes as low as 20 atmospheres, more typically 
                      50 to over 100
                      atmospheres. These lamps are an explosion hazard!
                      Mercury short arc lamps are used when a compact, intense 
                      source of UV is
                      needed or where one cannot have the high voltage starting 
                      pulses needed for
                      xenon short arc lamps. Mercury short arc lamps are 
                      slightly more efficient
                      than xenon ones. The pressure in a mercury short arc lamp 
                      does not need to
                      be as high for good efficiency as in a xenon one, but is 
                      still tremendous.
                      Xenon short arc lamps are more common than mercury ones, 
                      since they do not
                      require time to warm up the way mercury lamps do and have 
                      a daylight-like
                      spectrum. A disadvantage of xenon is the requirement of a 
                      very high voltage
                      starting pulse - sometimes around 30 kilovolts!
                      Xenon short arc lamps are used for movie projection and 
                      sometimes for
                      searchlights. Lower wattage ones are used in specialized 
                      devices such as
                      endoscopes.
                      HMI lamps are metal halide lamps with a more compact and 
                      more intense arc.
                      The arc is larger and less intense than that of a short 
                      arc lamp. Typical
                      power input is hundreds of watts per centimeter of arc 
                      length, but gets to a
                      few kilowatts per centimeter in the largest ones.
                      HMI lamps are used in some spotlights. They are used in 
                      some endoscopes and
                      projection applications where the intensity of the HMI arc 
                      is adequate since
                      they cost less and last longer and are more efficient than 
                      true short arc
                      lamps.
                      There are all sorts of HMI and similar lamps, including 
                      HTI lamps and the
                      lamps used in HID auto headlights.
                      HID Automotive Headlights
                      First there were gas lamps, then there were electric 
                      bulbs, then sealed
                      beam, then halogen. Now, get ready for - drum roll please! 
                      - high intensity
                      discharge lamps with sophisticated controllers. High-end 
                      automobiles from
                      makers like BMW, Porsche, Audi, Lexus, and now Lincoln are 
                      coming equipped
                      with novel headlight technology. No doubt, such technology 
                      will gradually
                      find its way into mainstream automobiles - as well as 
                      other applications for
                      mortals.
                      Among the potential advantages of HID headlights are 
                      higher intensity,
                      longer life, superior color, and better directivity:
                         * Light intensity - HID lamps are about 3 times as 
                      efficient as halogen
                           lamps. Thus, even when the efficiency of the DC-DC 
                      converter is taken
                           into consideration, the lower power input can 
                      actually result in much
                           brighter headlights than are possible with halogen 
                      bulbs. This reduced
                           power also leads to cooler operation and less drain 
                      on the battery and
                           alternator.
                         * Lifespan - an HID lamp can be expected to last 2,700 
                      hours or more and
                           thus covered under the bumper to bumper warranty for 
                      100,000 miles. As
                           a practical matter, the HID lamp may outlast the 
                      automobile. Since
                           warranty replacement of headlights turns out to be a 
                      significant
                           expense, there is strong incentive to see this long 
                      lived technology
                           take off.
                         * Spectral output - the light from the HID lamp is 
                      richer in blue (and
                           more like daylight) than halogen bulbs. This turns 
                      out to enhance
                           reflectivity of signs and road markings.
                         * Beam pattern - the small arc size of the HID lamp 
                      permits the optical
                           system to be optimized to direct light more 
                      effectively to where it is
                           needed and prevent it from spilling over to where it 
                      is not wanted.
                      In order to make this practical - even for a $40,000 Lexus 
                      - special DC-DC
                      converter chips have been designed specifically with 
                      automotive applications
                      in mind. These, along with a handful of other basic 
                      electronic components,
                      implement a complete HID headlight control system.
                      The HID bulb itself is similar in basic design to 
                      traditional HID lamps: Two
                      electrodes are sealed in a quartz envelope along with a 
                      mix of solids,
                      liquids, and gasses. When cold, these materials are in 
                      their native state
                      (at room temperature) but are mostly gases when the lamp 
                      is hot. Starting of
                      these lamps may require up to 20 KV to strike an arc but 
                      only 50 to 150 V to
                      maintain it. Lamps may be designed to operate on either AC 
                      or DC current
                      depending on various factors including the size and shape 
                      of the electrodes.
                      A unique set of ballast operating parameters must be 
                      matched to each model
                      HID bulb.
                      Of all the problems that had to be addressed for HID 
                      headlights to become
                      practical (aside from the cost), the most significant was 
                      the warmup time.
                      As noted in the section: "High intensity discharge (HID) 
                      lamp technology",
                      common HID lamps require a warmup period of a few minutes 
                      before
                      substantially full light output is produced. This is, of 
                      course, totally
                      unacceptable for an automotive headlight both for cold 
                      start (imagine:
                      "Honey, I have to go cook the headlights") as well as when 
                      they need to be
                      blinked. The warmup problem was solved by programming the 
                      controller to
                      deliver constant power to the lamp rather than the more 
                      common nearly
                      constant current that would be provided by a traditional 
                      ballast. With this
                      twist along with a special lamp design, the lamp comes up 
                      to at least 750f
                      full intensity in under 2 seconds. The controller also 
                      provides 'hot strike'
                      capability for blinking (recall that HID lamps typically 
                      cannot be restarted
                      when hot). Thus, restarting a hot lamp is absolutely 
                      instantaneous.
                      While this technology is just beginning to appear, expect 
                      inroads (no pun
                      intended) into household, office, store, factory, and 
                      other area and work
                      lighting. The combination of high efficiency, long life, 
                      desirable spectral
                      characteristics, small size, and solid state reliability 
                      should result in
                      many more applications in the near future. The nearly 
                      instant starting
                      capability addresses one of the major drawbacks of small 
                      HID lamps.
                      If you have some time and money to spare:
                      (From: Declan Hughes (hughes@aero.tamu.edu).)
                      Check out: OSRAM Sylvania Products Inc.
                      They have a "sample" for sale at $250.00 for one lamp 
                      including the 12 VDC
                      electronic ballast. 42 W total power, 35 W light power, 
                      3,200/2,800 lm
                      output (there are two types, D2S and D2R), 2,000 hours 
                      rated lifetime, 91/80
                      lm/W luminous efficacy, 4,250/4,150 K color temperature, 
                      6,500 cd/cm^2
                      average luminance, 4.2 mm arc length, burning position 
                      horizontal +/- 10
                      deg., luminous flux after 1 sec. = 25%, max. socket temp. 
                      = 180 deg C, any
                      errors are mine.
                      For more info, look in Don Klipstein's Automotive HID Lamp 
                      File.
                      Substitution of Metal Halide Lamps?
                      The following was prompted by a request for info on 
                      replacing an (expensive)
                      250 watt metal halide lamp in a video projector with 
                      something else.
                      I would not substitute this lamp, for many reasons below:
                      The metal halide lamp requires a ballast. The ballast 
                      should only run a 250
                      watt metal halide lamp of the same arc voltage. You will 
                      have to measure the
                      arc voltage yourself after the lamp warms up, and do this 
                      without exposing
                      yourself to the nasty UV that some of these things emit 
                      but which does not
                      pass through glass. Arc voltages of many specialized metal 
                      halide lamps are
                      not widely published and may or may not be available from 
                      the lamp
                      manufacturer.
                      WARNING: The strike voltage on these may be several kV 
                      which will probably
                      obliterate your multimeter should the arc drop out and 
                      attempt to restart
                      while you are measuring it! Either the operating or strike 
                      voltage may
                      obliterate you should you come in contact with live 
                      terminals! (Special
                      metal halides probably usually only need a couple to a few 
                      kV. Xenon metal
                      halide automotive lamps need 6 to 12 kV to strike and 15 
                      to 20 kV for hot
                      restrike. The worst are short arc xenon that may use up to 
                      30 kV or more.)
                      Most metal halide lamps are AC types and some are DC and 
                      you can only use AC
                      lamps on AC output ballasts and DC lamps on DC output 
                      ballasts. Different
                      metal halide lamps may have different requirements for 
                      starting voltage
                      also.
                      If you match arc voltage, AC/DC type, and the ballast will 
                      start the lamp,
                      you might be in business but good chance not. Many 
                      projector lamps have
                      specific cooling requirements and some have specific 
                      burning position
                      requirements. Metal halide lamps may prematurely fail 
                      (possibly violently!)
                      if they overheat, in addition to being off-color. If 
                      overcooled, they are
                      more like mercury lamps and will be off-color and have 
                      reduced light output.
                      In addition, some metal halide lamps have a halogen cycle 
                      in them to keep
                      the inner surface of the bulb clean, and that may not work 
                      if the lamp is
                      overcooled and not enough of the chemicals in the bulb get 
                      vaporized. This
                      could also even make the lamp fail.
                      If you get the alternate lamp to operate satisfactorily, 
                      the arc may be in a
                      different location from that of the original lamp. The arc 
                      may be of a
                      different shape or size than that of the original lamp. 
                      This can affect your
                      projection. Your projection may not get much light or may 
                      have illumination
                      of only part of the picture.
                      The arc may have a different color or spectrum, which can 
                      affect the color
                      rendering of what's being projected. Metal halide arcs are 
                      often not of
                      uniform color, and if the alternate lamp has a less 
                      color-uniform arc than
                      the original lamp then your pictures may have strange 
                      color tints in them.
                      As for using a halogen instead of metal halide? You will 
                      get less light, as
                      well as problems from the filament having a different 
                      shape or size than the
                      original metal halide arc does. Most likely, the filament 
                      is larger or
                      longer than the arc and this will reduce the percentage of 
                      the light being
                      utilized. Should you try a halogen lamp hack, you will 
                      almost certainly have
                      to bypass the metal halide ballast. And halogen lamps emit 
                      more infrared
                      than metal halide lamps of the same wattage - you might 
                      overheat the source
                      of your image (e.g., LCD panel or transparency).
                      I would not recommend substituting a projector lamp for 
                      all of these
                      reasons. This should only be tried at your own risk and 
                      only by those that
                      are very familiar with all of the characteristics of the 
                      lamps in question -
                      including being familiar with burning position 
                      requirements, cooling
                      requirements, shape and size of the light-emitting region, 
                      etc.
                      Projector lamps in general, and especially specialized HID 
                      lamps, should be
                      used only in equipment made specifically to use the 
                      particular lamps in
                      question, or by those who know about these things well 
                      enough to make their
                      own ballasts and know the other messy things about these 
                      lamps. And you may
                      not save much by using a different lamp - specialized 
                      metal halide lamps are
                      all expensive.
                      And for anyone shopping for any sort of projector - look 
                      into price,
                      availability, and life expectancy of lamps!
----------------------------------------------------------------------------

Low Pressure Sodium   Lamps
                      Low pressure sodium lamps most efficient 
                      luminous efficacies as high as 180 lumens per watt.
                      consists of tube made of special sodium-resistant glass 
                      containing sodium and a neon-argon gas mixture.
                      tube rather large and must reach temperature around 300C 
                      tube bent into tight U-shape and enclosed in an evacuated
                      outer bulb in order to conserve heat. 
                      additional heat conservation measure, 
                      inner surface of outer bulb is coated with  material that
                      reflects infrared but passes visible light. 
                      material has traditionally
                      been tin oxide or indium oxide.
                      electrodes are coiled tungsten wire 
                      coated with thermionically emissive material, 
                      resemble electrodes of fluorescent lamps. Unlike
                      most fluorescent lamps, low pressure sodium lamps 
                      have only one electrical connection to each electrode 
                      and the electrodes cannot be preheated.
                      gas mixture is  "Penning" mixture, 
                      consisting mainly of neon with small amount of argon
                      Depending on who you listen to, this mixture is .5 to
                      2 percent argon, 98 to 99.5 percent neon. 
                      More argon-rich mixtures around
                      98-2 may be favored today since hot glass 
                      has some ability to absorb argon
                      from a low pressure electric discharge. 
                      Ideally mixture should be only a
                      few tenths of a percent argon, 
                      in order to ionize most easily and do so much
                      more easily than pure neon or pure argon.
                      significant surplus of sodium i
                      is contained in glass arc tube 
                      since  glass may absorb or react with some ofthe sodium. 
                      sodium vapor pressure controlled by temp 
                      of coolest parts of the arc tube. When
                      arc tube reaches a proper temperature, 
                      further heating is reduced by the
                      lamp's efficiency at producing light instead of heat.
                      arc tube has dimples in it, 
                      which are normally slightly cooler than the
                      rest of the arc tube. 
                      causes  sodium metal to collect in the dimples
                      instead of covering a larger portion of the arc tube
                      and blocking light.
                      low pressure sodium lamp 5 to 10 minutes to warm up.
                      light of low pressure sodium consists almost entirely of 
                      orange-yellow 589.0 and 589.6 nM sodium lines. light is 
                      monochromatic orange-yellow. 
                      -- end V1.34 --
                      -------------------------------------------------------------------
                      1. REFERENCES!!
                      I highly recommend the book by W. Elenbaas, "The High 
                      Pressure Mercury Vapor
                      Discharge", published in 1951 by North Holland Publishing 
                      Co., Amsterdam.
                      This book has lots of basic and advanced theory on high 
                      pressure mercury
                      lamps, some of which is applicable to other types of HID 
                      lamps.
                      After finding this book, you may want to look into others 
                      with similar call
                      numbers. Using the Library of Congress system, look into 
                      everything with
                      numbers around TK4000.
                      2. What are low and high pressure lamps?
                      In a high pressure lamp, the average kinetic energy of 
                      free electrons (also
                      known as electron temperature) is only slightly higher 
                      than the temperature
                      of the gas in the discharge. Both temperatures are 
                      similar, and one can
                      refer to a general temperature of the discharge. The 
                      electron temperature is
                      higher in order for the electrons to have the net effect 
                      of transferring
                      energy to the gas.
                      It is quite fair to think of the gas or vapor as a thermal 
                      radiator, which
                      is usually spectrally selective and radiating mainly in 
                      specific spectral
                      lines.
                      Typically, the discharge diameter is over 50 times the 
                      mean free path of an
                      electron. There is generally no non-thermal, non-optical, 
                      non-mechanical
                      interaction between the discharge and any container it is 
                      in, except at the
                      ends of the discharge.
                      In order to efficiently produce light, the power input 
                      must be much greater
                      than the heat conduction from the discharge, which is 
                      usually near or over
                      10 watts per centimeter of discharge length. Therefore, 
                      power input to a
                      high pressure lamp is usually near or over 20 watts per 
                      centimeter of
                      discharge length.
                      The above can all be satisfied even if the pressure is 
                      less than 1
                      atmosphere. It can even be satisfied in a nearly practical 
                      lamp with a
                      pressure of .1 atmosphere.
                      High pressure lamps are often referred to as High 
                      Intensity Discharge Lamps,
                      or HID lamps.
                      In a low pressure lamp, the electron and gas temperatures 
                      are very
                      different, and the pressure is generally below .05 
                      atmosphere. Power input
                      is generally near or less than 1 watt per centimeter.
                      2a. What's in a low pressure mercury or sodium lamp?
                      In a low pressure lamp with mercury or sodium vapor as an 
                      active ingredient,
                      the metal vapor is mixed with an inert gas, often neon or 
                      argon. The metal
                      vapor's pressure is usually well under 1/1000 atmosphere, 
                      or a fraction of a
                      mm. of Hg. The mixture is generally 1 percent or even as 
                      little as .1
                      percent metal vapor, 99 to 99.9 percent inert gas.
                      The desired spectral output generally results from atomic 
                      transitions that
                      terminate in the atom's "ground" or unexcited state. This 
                      means that most of
                      the metal vapor atoms, since they are not excited, can 
                      easily absorb this
                      radiation. Therefore, you don't want too much metal vapor. 
                      The inert gas
                      largely determines electrical characteristics, mainly by 
                      controlling the
                      mean path traveled by electrons between collisions. The 
                      gas also reduces
                      collisions of electrons, ions, and excited metal vapor 
                      atoms into the lamp's
                      walls.
                      2B. How do lamps with 1 percent or less metal vapor 
                      produce only or mainly
                      metal spectral output?
                      The excited states of the metal vapor atoms are mainly, 
                      usually entirely at
                      lower energy levels than those of the inert gas atoms. 
                      Free electrons in the
                      lamp with enough kinetic energy to excite anything 
                      generally only have
                      enough to excite the metal vapor atoms.
                      3. Negative resistance and why you need a ballast to limit 
                      current
                      In a high-pressure lamp, if current increases, the arc 
                      gets hotter. This
                      tremendously increases the concentration of ions and free 
                      electrons, making
                      the arc that much more conductive. The conductivity of the 
                      arc increases
                      enough that the voltage across the arc usually stays about 
                      the same or even
                      decreases if the current is increased.
                      In a low-pressure lamp, a variation of this causes the 
                      same thing. If you
                      double the current, you usually roughly double the 
                      concentration of excited
                      gas atoms and free electrons. The concentration of ions 
                      must match that of
                      free electrons but each excited atom is bombarded twice as 
                      much by free
                      electrons (remember, there are twice as many electrons 
                      around for an excited
                      atom to see). The average kinetic energy of the free 
                      electrons must decrease
                      so that ion concentration is also only roughly doubled. To 
                      get slower free
                      electrons, the electric field in the discharge (and 
                      voltage across the
                      discharge) must decrease.
                      In either case, it is not a good idea to connect the lamp 
                      directly to a
                      voltage source. Once the lamp starts conducting, 
                      increasing current will
                      increase the lamp's conductivity, allowing more current to 
                      flow. This
                      process does not level off until one of the following 
                      happens:
                      1. A large fraction of easily ionizable atoms are ionized,
                      2. The concentration of ions/free electrons is so high 
                      that more of these
                      somehow impairs mobility of free electrons,
                      3. The power supply's or wiring's limitations limit the 
                      current.
                      At this point, the current is usually around or over 100 
                      amps or so, and
                      will likely blow fuses/pop breakers, and is certainly not 
                      good for the lamp.
                      The term "negative resistance" refers to a decrease in 
                      voltage across the
                      lamp resulting from an increase in current through the 
                      lamp.
                      4. Why the light from many discharge lamps makes red 
                      things look dull
                      Mercury lamps, most metal halide lamps, most sodium lamps, 
                      and "cool white",
                      "white", and "warm white" fluorescent lamps have a 
                      shortage of red and green
                      light in their spectral output. These lamps also have a 
                      surplus of yellow
                      and/or orange-yellow. Since red plus green looks yellow, 
                      taking away red and
                      green and adding yellow do not affect how the lamp's color 
                      looks.
                      Nearly all yellow objects reflect red, orange, yellow, and 
                      green. Increasing
                      yellow output and decreasing red and green does not change 
                      how yellow
                      objects look.
                      However, red objects generally reflect mostly just red 
                      light. With the
                      shortage of red light, these look darker. If they are not 
                      pure red in color,
                      they will not only look darker but also less red in color.
                      Unphosphored (clear bulb) high pressure mercury lamps are 
                      especially bad at
                      this, since they make very nearly no red light at all.
                      This is not a problem with most compact fluorescent lamps, 
                      most 1-inch
                      diameter 4-foot lamps, and other fluorescent lamps that 
                      have "rare-earth"
                      phosphors. These phosphors, unlike those in older formula 
                      fluorescent lamps,
                      produce a strong, narrow orangish red spectral band and a 
                      strong, somewhat
                      narrow, slightly yellowish green one, with little in 
                      between. Under these
                      lamps, reds usually look near normal, or slightly 
                      orangish, or slightly
                      excessively bright. Greens often also look slightly 
                      brighter under these
                      lamps than under old formula "cool white" and "warm white" 
                      fluorescent
                      lamps.
                      5. Why photos taken under discharge lamps often look 
                      blue-green
                      The problem here is the fact that film and human eyes have 
                      different
                      spectral response. Human eyes are quite sensitive to the 
                      short wave end of
                      the red range of the visible spectrum, but not to the long 
                      wave end. Most
                      color film responds about the same to shorter and longer 
                      red wavelengths.
                      Most of the red light from fluorescent lamps, metal halide 
                      lamps, sodium
                      lamps, and phosphored mercury lamps is of shorter red 
                      wavelengths. These
                      lamps do not emit much of the longer red wavelengths. This 
                      maximizes red
                      sensation by the eye for a given amount of actual light. 
                      Producing
                      less-visible longer red wavelengths detracts from 
                      maximizing luminous
                      efficacy of the lamp, so this is minimized.
                      Therefore, lamps make a surplus of red wavelengths to 
                      which the eye is more
                      sensitive than film is, and a shortage of the red 
                      wavelengths to which film
                      is more sensitive than human eyes. This results in the 
                      film seeing red less
                      than human eyes do, and this makes photos look 
                      blue-greenish.
                      6. Arc and glow discharges explained!
                      Electrons normally don't just move or flow from a 
                      conductor into a gas.
                      Something has to make this happen. Explained below are 
                      ways for this to
                      happen.
                      In a glow discharge, positive ions bombarding the cathode 
                      dislodge electrons
                      from the cathode material. There is a substantial electric 
                      field near the
                      cathode that accelerates ions toward the cathode to make 
                      this happen. The
                      whole process tends to complicate itself, resulting in a 
                      double layer of
                      glow around the cathode, thin dark spaces underneath and 
                      between these
                      layers, and a more substantial dark space between all of 
                      this and either the
                      anode or the main body of the discharge, whichever comes 
                      first. In neon glow
                      lamps, the anode is so nearby that no main discharge body 
                      occurs.
                      "Neon" signs are longer, so a main discharge body occurs. 
                      Since these
                      operate on AC, each end has a significant dark space only 
                      half the time, so
                      these regions are a bit dim rather than dark.
                      There is generally a natural current density in the 
                      cathode process,
                      generally around a milliamp to .1 amp per square 
                      centimeter, depending on
                      the gases involved, the pressure thereof, and the cathode 
                      material. A glow
                      discharge at this intensity is a "normal glow". Decreasing 
                      the current
                      causes the cathode's glowing layers to cover only part of 
                      the cathode. In
                      this case, the glow often moves around, causing a 
                      flickering effect.
                      If the current is more than enough to cause the cathode to 
                      be covered with
                      glow, (or if the glowing layers are forced into a thinner 
                      layer of space
                      than they normally use), abnormal glow results. The 
                      voltage drop of the
                      cathode process (this voltage is known as the "cathode 
                      fall") will be higher
                      than normal. This causes ions to bombard the cathode 
                      harder than usual. This
                      increases "sputtering", or dislodging of cathode material 
                      atoms. Sputtering
                      effectively "evaporates" cathode material and often causes 
                      darkening of the
                      lamp's inner surface.
                      Sputtering occurs more easily at higher cathode 
                      temperatures. It is
                      generally recommended to neither have significantly 
                      "abnormal" glow nor
                      significant temperature rise in the cathode, and 
                      especially not both of
                      these combined.
                      The cathode fall of normal glow is usually 50 to 90 volts 
                      for neon, argon,
                      krypton, xenon, or mixtures including significant amounts 
                      of any of these
                      gases. Some metal vapors may have somewhat lower cathode 
                      falls. Nitrogen and
                      some other gases have high cathode falls usually near or 
                      even well over 100
                      volts.
                      The cathode process in most HID lamps and fluorescent 
                      lamps is the
                      thermionic arc. In this process, at the proper high 
                      temperature, some
                      material in the cathode fails to keep a grip on its 
                      electrons. Therefore,
                      electrons simply flow from the cathode to the gas. The 
                      cathode fall is
                      usually around 10 volts, and the heat dissipated in this 
                      process keeps the
                      cathode hot enough to let electrons flow from it to the 
                      gas.
                      The current density at the cathode process of a thermionic 
                      arc is generally
                      in the tens or hundreds of amps per square centimeter of 
                      active cathode
                      surface, but can occaisionally be as low as around an amp 
                      per square
                      centimeter if a heat source other than the arc heats the 
                      cathode.
                      Another arc process is the cold cathode arc. In this 
                      process, ions bombard
                      the cathode material and dislodge electrons from it. This 
                      seems similar to
                      the glow discharge, but the effect is quite different. The 
                      current density
                      in the cathode process is usually hundreds or thousands of 
                      amps per square
                      centimeter. The cathode fall is usually near the 
                      ionization potential of the
                      cathode material or the main active gas ingredient, 
                      whichever is lower (for
                      a minimum) to twice whichever is higher (for a maximum). 
                      Substantial
                      sputtering may occur, especially if the cathode is hot. 
                      Cold tungsten is
                      usually reasonably tolerant of this, permitting the use of 
                      this process in
                      xenon flashtubes.
                      An arc is often not entirely thermionic nor cold-cathode, 
                      but one of these
                      processes is usually dominant.
                      If a hot-cathode lamp is underpowered, the cathode is not 
                      as able to emit
                      electrons by the thermionic process, and significant 
                      cold-cathode arc
                      process may occur. This can cause excessive sputtering. 
                      Starting a
                      hot-cathode lamp also results in some of this as the 
                      cathode warms up.
                      Overpowering a hot-cathode lamp can simply overheat the 
                      cathodes.
                      Because of this, it is generally advised to start 
                      fluorescent and HID lamps
                      as infrequently as practical and to neither overpower nor 
                      underpower them.
                      This makes it difficult to dim fluorescent and HID lamps 
                      significantly
                      without being hard on their cathodes.
                      There are some special dimming ballasts for some 
                      fluorescent lamps. These
                      dissipate power into the cathodes to maintain a workable 
                      thermionic process
                      when these lamps are dimmed. It is recommended to only dim 
                      fluorescent lamps
                      with appropriate ballasts, and to use these dimming 
                      ballasts only with the
                      lamps they were designed to safely dim.
                      7. What do high-pressure sodium lamps have?
                      One thing these lamps have is a mixture of mercury and 
                      sodium, rather than
                      just sodium. If only sodium was in these, the voltage 
                      across the lamp would
                      be excessively low. Making the arc tube longer to increase 
                      voltage drop
                      would also increase the watt-per-centimeter loss 
                      (explained below in section
                      8). A higher sodium vapor pressure would also increase the 
                      voltage drop, but
                      would broaden the sodium's emission band to the point that 
                      much of the
                      spectral output is nearly infrared. This detracts from 
                      maximum most-visible
                      light output.
                      Also, a mercury-sodium mixture conducts heat less than 
                      pure sodium vapor.
                      This reduces thermal conduction of energy away from the 
                      arc (The
                      watt-per-centimeter loss).
                      Another thing: Hot sodium is very highly chemically 
                      reactive. Some of the
                      sodium is lost as the lamp ages, either permeating through 
                      the arc tube or
                      chemically becoming part of it. Therefore, a surplus of 
                      sodium is included
                      in the arc tube. The sodium vapor pressure is controlled 
                      by the temperature
                      of the "amalgam reservoir(s)" of the arc tube, where any 
                      unevaporated
                      mercury and sodium reside. Proper lamp operation depends 
                      on the amalgam
                      reservoir(s) being at or near a proper temperature.
                      7a. Why do aging sodium lamps sometimes cycle repeatedly 
                      on and off?
                      The sodium vapor pressure is controlled by the temperature 
                      of the amalgam
                      reservoirs at the ends of the arc tube. As the lamp ages, 
                      the ends of the
                      arc tube get darkened, and they absorb light. This makes 
                      them hotter.
                      Therefore, the amalgam reservoirs get hotter. This 
                      increases the sodium
                      vapor pressure in the arc tube, leading to different 
                      electrical
                      characteristics. When this effect becomes excessive, the 
                      arc in the arc tube
                      goes out. The arc tube must cool before the vapor in it is 
                      thin enough to
                      restrike an arc.
                      Aging sodium lamps sometimes repeatedly turn on and off as 
                      the ends of the
                      arc tubes overheat, then cool off once the arc goes out. 
                      If a high pressure
                      sodium lamp repeatedly turns on and off, replacing the 
                      bulb with a new one
                      is usually all that is needed.
                      8. Thermal Conduction from High Pressure Arcs, the Watt 
                      per Centimeter Loss
                      When energy is dissipated into an arc, it largely leaves 
                      the arc by three
                      mechanisms:
                      1. Some is used by the cathode and anode fall mechanisms 
                      getting electrons
                      from metal to arc and vice versa. Nearly all of the energy 
                      here ends up
                      heating the electrodes. The anode fall is not always 
                      significant, the
                      cathode fall usually is. 2. Thermal conduction removes 
                      energy from the main
                      body of the arc. This ends up heating the arc's 
                      surroundings and any
                      container or arc tube.
                      3. Whatever energy enters the body of the arc (not lost in 
                      electrode falls)
                      and not thermally conducted from the arc is radiated.
                      Of course, it is desirable to minimize (1) and (2) and to 
                      maximize (3).
                      The electrode falls are generally a fairly constant 
                      voltage. Designing the
                      main body of the arc to have more voltage across it 
                      (higher voltage drop)
                      and use less current reduces the electrode losses.
                      However, there is a limit to practical arc voltages, since 
                      higher voltages
                      may require complicated equipment to supply them, and also 
                      higher pressure.
                      The thermal conduction loss is a major loss in many high 
                      intensity discharge
                      lamps, especially ones of lower wattages.
                      This loss varies with arc temperature, gas and vapor type, 
                      and is largely
                      linearly proportional to the length of the arc. However, 
                      this loss usually
                      does not vary much with the arc's diameter nor with the 
                      gas pressure. Often,
                      especially in mercury vapor lamps, the arc temperature is 
                      surprisingly
                      constant, and this leads to a surprisingly constant 
                      thermal conduction loss
                      from the arc, in watts per centimeter of arc length. This 
                      loss increases if
                      the arc tube size and/or gas pressure are great enough for 
                      convection to be
                      significant, and the nearly constant degree of this loss 
                      applies to typical
                      general purpose HID arcs that are many times longer than 
                      they are wide. The
                      loss is different for the nearly spherical arcs in some 
                      special HID lamps.
                      For typical mercury vapor lamps, the thermal conduction 
                      loss is generally
                      around 10 watts per centimeter. For high pressure sodium 
                      lamps, this loss is
                      less constant but generally near 10 watts per centimeter. 
                      This loss can vary
                      with the ratios of the mercury-sodium mix since sodium 
                      vapor conducts heat
                      more than mercury vapor does. For metal halide lamps, this 
                      loss is less
                      constant and generally greater (in watts per cm.) due to 
                      convection in the
                      short, wide arc tubes that are filled to a very high 
                      pressure.
                      The watt/cm. loss could be reduced by:
                      1. Using a shorter arc. This requires a higher pressure 
                      for the same arc
                      voltage. Also, the parts of the arc tube within one tube 
                      radius of the
                      electrodes are subjected to being darkened by 
                      evaporated/sputtered electrode
                      material, so it may not pay to have an arc length shorter 
                      than a few times
                      the arc tube diameter. Reducing the arc tube diameter 
                      would help this, but a
                      skinnier arc tube will get hotter from the same watts of 
                      heat per
                      centimeter. All of this combined impairs the design of 
                      economical
                      miniaturized HID lamps.
                      2. Fill the arc tube with a less thermally conductive 
                      material. Such
                      materials have larger and/or heavier molecules. Heavier 
                      molecules move more
                      slowly, larger size ones don't go as far between 
                      collisions. This favors use
                      of mercury and xenon as HID lamp ingredients.
                      Low-heat-conductivity gases and vapors should be gaseous 
                      at reasonable arc
                      tube temperatures, chemically stable or inert at all 
                      temperatures from below
                      freezing to the arc temperature, and not have major 
                      infrared or ultraviolet
                      emission lines that detract from efficiently radiating 
                      visible light. This
                      largely disqualifies polyatomic substances and the vapors 
                      of heavier alkali
                      metals.
                      For more information on this, look in the Elenbaas book 
                      mentioned above.
                      8a. Why is the temperature of a mercury arc so constant?
                      The amount of energy radiated from a "blackbody" (the 
                      ideal thermal
                      radiator) is proportional to the fourth power of the 
                      radiator's temperature.
                      Or, the temperature is proportional to the fourth root of 
                      the amount of
                      power being dissipated into the radiator.
                      Now, for two properties of high pressure mercury vapor 
                      that favor a more
                      extreme radiation-vs.-temperature relationship.
                      1. Mercury has major ultraviolet lines at wavelengths 
                      shorter than those
                      most favored by typical mercury arc temperatures. 
                      Increasing the temperature
                      shifts the spectral output towards shorter wavelengths, 
                      causing radiation at
                      these wavelengths to increase by more than the 4th power 
                      of the temperature.
                      2. Except in the shortest two major ultraviolet lines, the 
                      emissivity of
                      mercury vapor in its spectral lines increases with 
                      temperature. This causes
                      the mercury to radiate almost as well as a blackbody at 
                      its main emission
                      wavelengths if the temperature is high enough, and not 
                      radiate nearly as
                      well as a blackbody at lower temperatures. The result: 
                      radiation varying
                      more dramatically than temperature to the 4th power.
                      Why emissivity in these spectral lines varying with 
                      temperature? Because the
                      lower of the two electron orbits (energy levels) used to 
                      radiate these lines
                      are elevated orbits, not the "ground state" (unexcited 
                      state). The mercury
                      atom must be excited just to elevate an electron into the 
                      lower level of
                      transitions responsible for all major spectral lines 
                      except two short-wave
                      ultraviolet ones. This is also why mercury vapor tends to 
                      have no absorption
                      lines except the two shortwave UV ones.
                      With radiation increasing very dramatically with a slight 
                      increase in arc
                      temperature, and decreasing dramatically with a slight 
                      decrease in arc
                      temperature, it is easy to see why mercury arcs have a 
                      nearly constant
                      temperature in most cases. This temperature is around 
                      5500-5900 Kelvin.
                      Many other substances do the same thing, but typically 
                      don't regulate the
                      arc temperature to the degree that mercury vapor does. For 
                      example, sodium's
                      main yellow emission line is at a wavelength slightly 
                      shorter than most
                      favored by a typical sodium arc temperature, and high 
                      pressure sodium lamps
                      also have significant spectral lines resulting from 
                      transitions between
                      elevated electron orbits. High pressure sodium arcs are 
                      not as constant in
                      temperature as mercury arcs, with arc center temperatures 
                      generally in the
                      low to mid 4,000's degrees Kelvin.
                      9. Why lamp voltage cannot exceed approx. 3/4 of 
                      line/open-circuit voltage
                      Here's why: (Example using a simple choke or inductor or 
                      "reactor" ballast)
                      Suppose you have the lamp and the choke in series, powered 
                      by a variable
                      current source, as opposed to a variable voltage source. 
                      Suppose you had
                      optimum cathode heating regardless of current through the 
                      lamp. Due to the
                      "negative resistance" characteristic most gas discharges 
                      have, the voltage
                      across the tube will increase as current is decreased. In 
                      fact, there will
                      be a point at which the combined tube-ballast voltage is 
                      minimized. This has
                      some voltage across the choke ballast, meaning the voltage 
                      across the lamp
                      is less than the line voltage.
                      The minimum line voltage to work at all is typically 
                      approx. 1.2 to 1.25
                      times the lamp voltage. For reasonably good, stable and 
                      reliable operation,
                      the voltage across the lamp should generally not exceed 
                      approx. 2/3 of the
                      line voltage.
                      With a "high-leakage-reactance transformer" ballast, the 
                      lamp voltage needs
                      to be correspondingly less than the "open circuit" (no 
                      load) output voltage
                      of the transformer.
                      10. What's with those aquarium metal halide lamps of 
                      extreme color
                      temperature?
                      Every so often, someone gets the idea that the arc 
                      temperature in a metal
                      halide lamp is about the same as the color temperature. 
                      That is not true.
                      The arc temperature is almost always in the 4200 to 5400 
                      Kelvin range. The
                      color temperature merely indicates the temperature that a 
                      "blackbody" (ideal
                      thermal radiator) must be to glow with the same or 
                      closest-possible color.
                      The color of a metal halide lamp depends on what metals 
                      are used in the
                      metal halides (usually iodides) and how much halide 
                      vaporizes. Lower color
                      temperatures in the 3000 to 3500 Kelvin range indicate 
                      orange-yellowish
                      shades of white, and the vapor in these lamps is rich in 
                      sodium but also has
                      smaller traces of scandium and sometimes thallium. Most 
                      metal halide lamps
                      contain sodium and scandium halides and have a color 
                      temperature near 4100
                      Kelvin (basically plain white). Some have less sodium and 
                      more scandium, and
                      sometimes also other more blue-glowing metals like indium, 
                      and therefore
                      have a more blue color. I have seen some metal halide 
                      lamps that seemed to
                      have more indium than any other metal in halide form, and 
                      these were more
                      blue in color. I have heard of metal halide lamps with 
                      color temperatures as
                      high as 20,000 Kelvin - and this is not hard to do even 
                      with an arc
                      temperature well below 5500 Kelvin.
                      Indium-rich metal halide lamps are sometimes used to 
                      illuminate aquariums
                      that have live coral, since coral needs deep-blue 
                      wavelengths for proper
                      health.
                      11. Why do some fluorescent lamp starters and neon lamps 
                      need light to
                      start?
                      A few people get annoyed at fluorescent lamps that refuse 
                      to start unless
                      some light hits the fixture. Why should there be a light 
                      that refuses to
                      turn on when it is dark?
                      Here is the explanation. These fluorescent fixtures have 
                      starters. The
                      starter is usually of the "glow switch" type. The glow 
                      switch starter is a
                      glow lamp with a bimetal strip for one electrode. The 
                      bimetal strip changes
                      shape as it heats up, and contacts the other electrode and 
                      temporarily
                      becomes a short circuit. For more information on 
                      fluorescent lamp circuits,
                      go to the Fluorescent Lamp General Info Page.
                      But why the light sensitivity? The glow lamp in the 
                      starter may be hard to
                      ionize at normal line voltage. Sometimes light hitting the 
                      electrodes of the
                      glow lamp can help via the photoelectric effect. Light 
                      hitting the
                      electrodes can dislodge or at least loosen a few electrons 
                      of the electrode
                      material's atoms. Some starters have holes in them, which 
                      let stray light in
                      to help.
                      Some starters have been made with easier-ionizing gas in 
                      them, but have been
                      prone to ionizing too easily. They ionized instead of the 
                      fluorescent tube
                      at times when the tube should have struck. Other starters 
                      have had
                      radioactive material in them to assist starting, but many 
                      people do not like
                      radioactive things around them.
                      Some neon lamps do this also, normally when they have aged 
                      past their
                      expected life. This is usually a characteristic of "high 
                      intensity" neon
                      lamps such as NE-2H, which have a reddish orange color and 
                      are filled with
                      pure neon. The electrodes are coated with material 
                      favorable to a glow
                      discharge, but the electrodes wear out and either higher 
                      voltage or the
                      photoelectric effect is needed to make them start. These 
                      lamps often flicker
                      when there is light and stay out when it is dark. Neon 
                      lamps with a
                      neon-argon mixture start more easily, but are dimmer. They 
                      have a
                      non-reddish orange color. They usually work reliably until 
                      they are too dark
                      from sputtered electrode material to be useful.
                      If you replace a neon lamp, be sure that the dropping 
                      resistor for an NE-2H
                      is at least 33K ohms for use with 120 volts AC. It is 
                      common to use 22K for
                      more light, but this compromises the life of the NE-2H. If 
                      you replace an
                      NE-2H with an NE-2 (easier starting), be sure to use a 
                      much higher dropping
                      resistor, at least 150K ohms and preferably at least 180K 
                      for use with 120
                      volts AC. Light output will be low.
                        ------------------------------------------------------------------------
                      Back up to Don's Main Lighting Page.
                      Back up to Don's Home Page.
                        ------------------------------------------------------------------------
                      Written by Don Klipstein.
                      Please read my Disclaimers.
                      Please read my Copyright info.
                      DC-Output, Constant Wattage 12 Volt Mercury Ballast!
                      Please read this article in its entirety before 
                      constructing this.
                      CAUTION - The following material gets quite technical at 
                      times, the device
                      below makes high voltages that can kill you, and if things 
                      go wrong it is
                      easy to make lots of smoke, custom and/or homebrew ferrite 
                      core inductors
                      are necessary, this circuit can be abusive to mercury 
                      lamps, mercury lamps
                      should be in suitable enclosed fixtures in case they 
                      explode. I recommend
                      this as a project only for those with prior electronic 
                      project and
                      electronic repair experience.
                      Corrections, additions, and questions to (don@misty.com). 
                      DO NOT use this
                      with metal halide or sodium lamps, since these lamps do 
                      not like DC and
                      metal halide lamps are less tolerant of constant-wattage 
                      warmup than mercury
                      lamps.
                      Below is a schematic for a DC output, nearly constant 
                      wattage circuit to
                      power mercury vapor lamps from 12 to 14 volts DC. The 
                      overvoltage
                      detection/handling circuit is shown separately below the 
                      main portion of
                      this schematic for clarity, but must be included. See the 
                      component
                      descriptions following the schematics for values and 
                      descriptions.
                      See other instructions following the component 
                      descriptions. It is important
                      to test for proper operation and proper power output.
                      This electronic ballast will give a mercury vapor lamp 
                      nearly constant
                      wattage despite variations in the voltage across the lamp. 
                      This will give
                      the lamp excessive current during warmup, when the voltage 
                      across the lamp
                      is less. An advantage of this is accelerated warmup of the 
                      lamp. A
                      disadvantage is overheating of the electrodes, especially 
                      the positive
                      electrode. Expect some significant discoloration around 
                      the positive
                      electrode, which will partially evaporate after several 
                      minutes to an hour
                      of use fully warmed up. Some permanent discoloration will 
                      remain.
                      I have found this discoloration quite severe with the 
                      Philips 40/50 watt
                      mercury lamp, but quite tolerable with 100 and 175 watt 
                      lamps. Please beware
                      that after the positive electrode has been abused a few 
                      times with constant
                      wattage warmup, it is likely to never work well in the 
                      future as a negative
                      electrode.



                        ------------------------------------------------------------------------
Fluorescent Fixture   Wiring Diagrams
                      Wiring for Preheat Fluorescent Fixtures
                      diagram for a typical preheat lamp - one that
                      uses a starter or starting switch.
                                    Power Switch    +-----------+
                       Line 1 (H) o------/ ---------|  Ballast  |-----------+
                                                    +-----------+           |
                                                                            |
                                            .--------------------------.    |
                       Line 2 (N) o---------|-       Fluorescent      -|----+
                                            | )         Tube         ( |
                                        +---|-         (bipin)        -|----+
                                        |   '--------------------------'    |
                                        |                                   |
                                        |          +-------------+          |
                                        |          |   Starter   |          |
                                        +----------| or starting |----------+
                                                   |   switch    |
                                                   +-------------+
                      some preheat ballasts use.  type was found on a
                      F13-T5 lamp fixture. types used for 30 and 40 watt preheat
                      lamps.3-lead preheat ballast volt-boosting "high leakage
                      reactance autotrans"  if voltage across tube is much over
                      approx. 60 percent of line voltage.                       
                                    Power Switch   +-------------+
                       Line 1 (H) o------/ --------|A  Ballast   |
                                        +----------|B           C|----------+
                                        |          +-------------+          |
                                        |                                   |
                                        |   .--------------------------.    |
                       Line 2 (N) o-----+---|-       Fluorescent      -|----+
                                            | )         Tube         ( |
                                        +---|-         (bipin)        -|----+
                                        |   '--------------------------'    |
                                        |                                   |
                                        |          +-------------+          |
                                        |          |   Starter   |          |
                                        +----------| or starting |----------+
                                                   |   switch    |
                                                   +-------------+
                      Fluorescent Starter Operation
                      Starters may be either automatic or manual:
                         * Automatic - The common type are called a 'glow tube 
                      starter' (or just
                           starter) and contains a small gas (neon, etc.) filled 
                      tube and an
                           optional RFI suppression capacitor in a cylindrical 
                      aluminum can with a
                           2 pin base. While all starters are physically 
                      interchangeable, the
                           wattage rating of the starter should be matched to 
                      the wattage rating
                           of the fluorescent tubes for reliable operation and 
                      long life.
                           The glow tube incorporates a switch which is normally 
                      open. When power
                           is applied a glow discharge takes place which heats a 
                      bimetal contact.
                           A second or so later, the contacts close providing 
                      current to the
                           fluorescent filaments. Since the glow is 
                      xtinguished, there is no
                           longer any heating of the bimetal and the contacts 
                      open. The inductive
                           kick generated at the instant of opening triggers the 
                      main discharge in
                           the fluorescent tube. If the contacts open at a bad 
                      time - current near
                           zero, there isn't enough inductive kick and the 
                      process repeats.
                           Higher-tech replacements called 'pulse starters' may 
                      be available for
                           the simple glow tube type starter. These devices are 
                      pin compatible
                           devices and contain a bit of electronics that detect 
                      the appropriate
                           time to interrupt the filament circuit to generate 
                      the optimal
                           inductive kick from the ballast. So, starting should 
                      be more reliable
                           with few/no blink cycles even with hard-to-start 
                      lamps. They will also
                           leave used-up tubes off, without letting them blink 
                      annoyingly.
                         * Where a manual starting switch is used instead of an 
                      automatic starter,
                           there will be three switch positions - OFF, ON, START:
                              o OFF: Both switches are open.
                              o ON: Power switch is closed.
                              o START (momentary): Power switch remains closed 
                      and starting switch
                                is closed.
                           When released from the start position, the breaking 
                      of the filament
                           circuit results in an inductive kick as with the 
                      automatic starter
                           which initiates the gas discharge.
                      Wiring for Rapid Start and Trigger Start Fixtures
                      Rapid start and trigger start fixtures do not have a 
                      separate starter or
                      starting switch but use auxiliary windings on the ballast 
                      for this function.
                      The rapid start is now most common though you may find 
                      some labeled trigger
                      start as well.
                      Trigger start ballasts seem to be used for 1 or 2 small 
                      (12-20 W) tubes.
                      Basic operation is very similar to that of rapid start 
                      ballasts and the
                      wiring is identical. "Trigger start" seems to refer to 
                      "rapid starting" of
                      tubes that were designed for preheat starting.
                      The ballast includes separate windings for the filaments 
                      and a high voltage
                      starting winding that is on a branch magnetic circuit that 
                      is loosely
                      coupled to the main core and thus limits the current once 
                      the arc is struck.
                      A reflector grounded to the ballast (and power wiring) is 
                      often required for
                      starting. The capacitance of the reflector aids in initial 
                      ionization of the
                      gases. Lack of this connection may result in erratic 
                      starting or the need to
                      touch or run your hand along the tube to start.
                      A complete wiring diagram is usually provided on the 
                      ballast's case.
                      Power is often enabled via a socket operated safety 
                      interlock (x-x) to
                      minimize shock hazard. However, I have seen normal 
                      (straight) fixtures which
                      lack this type of socket even where ballast labeling 
                      requires it. Circline
                      fixtures do not need an interlock since the connectors are 
                      fully enclosed -
                      it is not likely that there could be accidental contact 
                      with a pin while
                      changing bulbs.
                      Wiring Diagram for Single Tube Rapid or Trigger Start 
                      Ballast
                      Below is the wiring diagram for a single lamp rapid or 
                      trigger start
                      ballast. The color coding is fairly standard. The same 
                      ballast could be used
                      for an F20-T12, F15-T12, F15-T8, or F14-T12 lamp. A 
                      similar ballast for a
                      Circline fixture could be used with an FC16-T10 or lamp 
                      FC12-T10 (no
                      interlock).
                                   Power Switch  +---------------------+
                       Line 1 (H) o----/ --------|Black Rapid/Trigger  |
                                      +----------|White     Start   Red|----+
                                      |  +-------|Blue     Ballast  Red|-+  |
                                      |  |       +-----------+---------+ |  |
                                      |  |               |               |  |
                                      |  |      Grounded | Reflector     |  |
                                      |  |     ----------+----------     |  |
                                      |  |    .-----------------------.  |  |
                                      |  +----|-    Fluorescent      -|--+  |
                                      +------x| )       Tube        ( |     |
                       Line 2 (N) o----------x|-(bipin or circline)  -|-----+
                                              '-----------------------'
                      Wiring Diagram for Two Tube Rapid Start Ballast
                      The following wiring diagram is for one pair (from a 4 
                      tube fixture) of a
                      typical rapid start 48 inch fixture. These ballasts 
                      specify the bulb type to
                      be F40-T12 RS. There is no safety interlock on this 
                      fixture. (A similar
                      scheme could also be used on a dual tube Circline fixture 
                      though slightly
                      different ratings may be needed for each tube since they 
                      would be of
                      different sizes.)
                           Power Switch  +--------------------+
                     Line 1 (H) o--/ ----|Blac Dual Tube   Red|-----------+
                     Line 2 (N) o--------|White    Rapid   Red|--------+  |
                                   +-----|Yellow   Start  Blue|-----+  |  |
                                   |  +--|Yellow  Ballast Blue|--+  |  |  |
                                   |  |  +-----------+--------+  |  |  |  |
                                   |  |            |             |  |  |  |
                                   |  |   Grounded | Reflector   |  |  |  |
                                   |  |    --------+--------     |  |  |  |
                                   |  |  .------------------.    |  |  |  |
                                   |  +--|-   Fluorescent  -|----+  |  |  |
                                   |  |  | )    Tube 1    ( |       |  |  |
                                   +-----|-     bipin      -|-------+  |  |
                                   |  |  '------------------'          |  |
                                   |  |  .------------------.          |  |
                                   |  +--|-   Fluorescent  -|----------+  |
                                   |     | )    Tube 2    ( |             |
                                   +-----|-     bipin      -|-------------+
                                         '------------------'
                      Schematic of Typical Rapid/Trigger Start Single Lamp 
                      Ballast
                      This ballast is marked "Trigger Start Ballast for ONE 
                      F20WT12, F15WT12,
                      F15WT8, or F14WT12 Preheat Start Lamp. Mount tube within 
                      1/2" of grounded
                      metal reflector".
                      Voltages were measured with no bulb installed with safety 
                      interlock
                      bypassed.
                      Internal wiring has been inferred from resistance and 
                      voltage measurements.
                      The lossy autotransformer boosts line voltage to the value 
                      needed for
                      reliable starting with the filaments heated. It is assumed 
                      that part of the
                      magnetic circuit is loosely coupled so that putting the 
                      lamp between Red/Red
                      and Blue/White results in safe current limited operation 
                      once the arc has
                      struck.
                      A complete fixture wiring diagram like those shown in the 
                      section: Wiring
                      for Rapid Start and Trigger Start Fixtures will probably 
                      be provided on the
                      label.
                      Numbers in () are measured DC resistances.
                                    Red o--------------------------+
                                            8.5 V    Filament 1 (5) )||  
                                    Red o----------------------+---+ ||
                                             82.5 V            |     ||
                                                               +     ||
                                   Stepup  winding/choke is     )||==||  
                                   loosely coupled to main (37) )||  ||   
                                   magnetic  circuit            )||==||  
                                                               +     ||
                                                               |     ||
                         +--> Black (H) o----------------------+---+ ||
                         |               Primary  of starting       )|| 
                                          106.5 V              (31) )|| 
                       115 V             autotransformer            )||
                                   Blue o--------------------------+ ||
                         |                  8.5 V  Filament 2   (3) )||  
                         +--> White (N) o-----------o/o------------+  |
                                                 Interlock            |
                              Green (G) o-----------------------------+
                      Schematic for Rapid Start Ballast with Isolated Secondary
                      As noted, rapid start fixtures do not have a separate 
                      starter or starting
                      switch but use auxiliary windings on the ballast for this 
                      function. Here is
                      the schematic for a typical 1-tube rapid start fixture 
                      including the
                      internal wiring of the ballast.
                      This ballast includes separate windings for the filaments 
                      and a high voltage
                      winding that is on a branch magnetic circuit that is 
                      loosely coupled and
                      thus limits the current once the arc is struck. It is not 
                      known if this
                      design is common. The isolated secondary and separate high 
                      voltage winding
                                            would make it more expensive to 
                      manufacture.
                      A complete fixture wiring diagram like those shown in the 
                      section: Wiring
                      for Rapid Start and Trigger Start Fixtures will probably 
                      be provided on the
                      label.
                                  +-------+
          Power Switch ||======||(        |
Line 1 (H) o---/ ----+ ||      ||(   +----+---------o    to both pins
                      )||      ||(  ( filament winding   on one end
                      )||      ||(   +--------------o
                      )||      ||(     HV winding       Grounded reflector
                      )||      || +=----^^^^^^^-------------------------+
                      )||      ||(                                     _|_
                      )||      ||(   +--------------o                   -
                      )||      ||(  ( filament winding   to both pins
Line 2 (N) o---------+ ||      ||(   +----+---------o    on other end
                       ||======||(        |
                                  +-------+
                               Loose magnetic coupling in the ballast core 
                      results
                               in leakage inductance for current limiting.
                      Schematic of Rapid Start Dual Lamp Ballast
                      This ballast is marked "Rapid Start Ballast for TWO 
                      F40WT12 Lamps. Mount
                      tubes within 1/2" of grounded metal reflector". This 
                      circuit was derived
                      from the measurements listed in the section: Measurements 
                      of a Dual Tube
                      Rapid Start Ballast.
                      The autotransformer boosts line voltage to the value 
                      needed for reliable
                      starting with the filaments heated. The series capacitor 
                      of approximately 4
                      uF is used instead of leakage inductance to limit current 
                      to the tubes.
                      Leakage inductance from loose magnetic coupling is used to 
                      smooth the
                      waveform of current flowing through the tubes. The .03 uF 
                      capacitor provides
                      a return path during starting to the yellow filament 
                      winding but is not
                      really used during normal operation.
                      Numbers in () are approximate measured DC resistances.
                      Red 1 o--------------------------+
                                8.5 V              (.5) )|| Tube 1 Filament 1
                      Red 2 o----------------------+---+ ||
                                                  _|_    ||
                                             4 uF ---    ||
                                                                |     ||
                                                                +---+ ||
                                               )||
                                               )||
                                               )|| HV winding
                                               )||
                                               )||
                                +---------+---+ ||
                                |        _|_    ||
                                | .03 uF ---    ||
                                |         |     ||
            Yellow o----------------------+---+ ||
                       8.5 V    |         (.5) )|| Tubes 1 and 2 filament 2
            Yellow o--------------------------+ ||
                                |               ||
                                |               ||
            Blue 1 o------------+-------------+ ||
                       8.5 V              (.5) )|| Tube 2 filament 1
            Blue 2 o--+-----------------------+ ||
                      |                         ||
    +--> Black (H) o--+-----------------------+ ||
    |                                          )|| Primary of
  115 V                                   (13) )|| autotransformer
    |                                          )||
    +--> White (N) o------------o/o-----------+ ||
                            Interlock           ||
                                                 |
         Green (G) o-----------------------------+
                      Measurements of Dual Tube Rapid Start Ballasts
                      One is a Universal, the other is a Valmont.
                      (Measurements made with Radio Shack multimeter)
                      Resistance:
                          Measurement            Universal        Valmont
                      ------------------------  -----------     -----------
                        White-Black                 13              13
                        Between blues               .5              .55
                        Between reds                .5              .55
                        Between yellows             .5              .6
                        Black to closer blue       <.1             <.1
                        Blue-red                   open            open
                        Blue-yellow                open             5 M
                        Red-yellow                 open            20 M
                      Capacitance:
                        Blue-red                   ~4 uF         ~3.5 uF
                        Blue-yellow              ~.03 uF
                        Red-yellow               ~.03 uF
                      Primary current, (not true RMS), various secondary load 
                      conditions:
                        Secondary open            .32 A           .35 A
                        60W 120V incandescent bulb.75 A           .63 A
                        Short                     .48 A           .53 A
                      Heater voltage:                   not measured    approx. 
                      8 V, unsteady
                      surprisingly independent
                                                                        of 
                      secondary load
                      Open circuit output voltage voltage (from one red wire to 
                      one blue one,
                      highest reading of four combinations):
                        Red-Blue                           270 V                 
                      275 V
                      Fluorescent Lamps in Series?
                      This is not possible where line voltage is 105 to 125 VAC 
                      because this is
                      not sufficient to sustain the discharge where two lamps 
                      are in series.
                      Special dual lamp ballasts are required.
                      However, where the line voltage is 220 VAC, it is 
                      possible:
                      (From: andrew@cucumber.demon.co.uk (Andrew Gabriel)
                      Here in UK (and probably all 220 to 250V areas), this is 
                      common:
                                          =======
                              L o---+-----^^^^^^^-------+ +-----+
                                    |     Ballast       | |     |
                                    |   (Inductor)     +|-|+    |
                                    |                  | - |    |
                                    |                  |   |   +-+
                                    |           Tube 1 |   |   |S| Glow Starter
                                    |                  |   |   +-+
                                    |                  | - |    |
                                    |                  +|-|+    |
                                    |                   | |     |
                                   _|_ Power Factor     | +-----+
                                   ___ Correction       |
                                    |  Capacitor        | +-----+
                                    |                   | |     |
                                    |                  +|-|+    |
                                    |                  | - |    |
                                    |                  |   |   +-+
                                    |           Tube 2 |   |   |S| Glow Starter
                                    |                  |   |   +-+
                                    |                  | - |    |
                                    |                  +|-|+    |
                                    |                   | |     |
                              N o---+-------------------+ +-----+
                                            Fluorescent Lamps in Parallel?
                      Like most gas discharge tubes, fluorescent lamps are 
                      negative resistance
                      devices. Therefore, it isn't possible to put more than one 
                      lamp in parallel
                      and get them both to light - additional components are 
                      needed. The following
                      applies mostly to magnetic ballasted fixtures. Where 
                      electronic ballasts are
                      used, all sorts of games can be played to implement wierd 
                      configurations!
                      Multiple lamp fixtures in countries with 110 VAC power 
                      usually have special
                      ballasts with separate windings for this purpose. Where 
                      220 to 240 VAC is
                      available, it may be possible to put multiple lamps in 
                      series with
                      individual starters. See the section: Fluorescent Lamps in 
                      Series?.
                      However, there is at least one application where putting 
                      two lamps is
                      parallel makes sense: light fixtures in hard-to-reach or 
                      safety-critical
                      areas where redundancy is desirable. With only minor 
                      modifications at most,
                      a conventional single lamp ballast can be connected to a 
                      pair of lamps in
                      such a way that only one will light at any given time. 
                      (Which one actually
                      starts could be random without additional circuitry, 
                      however.) If either
                      lamp burns out or is removed, the other will take over.                       
                      The ballast must
                      provide enough power to the filaments for starting but 
                      once started, the                      
                      lamp that is on will operate normally and there should be 
                      no degradation                       
                      in
                      performance or expected lamp life (except to the extent 
                      that the unlit                      
                      lamp's filaments might be kept hot).                      
                      The following is just a suggestion - I have not confirmed 
                      if or with which
                      model ballasts these schemes will work!
                      For rapid start ballasts, this could be as simple as 
                      wiring all connections
                      to the lamps in parallel - if the ballast has enough 
                      current available to
                      power both sets of filaments for starting. For trigger 
                      start ballasts, the
                      filament power is not an issue so it should be even 
                      easier:
                             Power Switch +---------------------------+
                 Line 1 (H) o----/ -------|Black   Rapid/Trigger      |
                                    +-----|White       Start       Red|------+
                                    |  +--|Blue       Ballast      Red|---+  |
                                    |  |  +--------------+------------+   |  |
                                    |  |               |                  |  |
                                    |  |               +---------------+  |  |
                                    |  |     Grounded  | Reflector     |  |  |
                                    |  |     ----------+----------     |  |  |
                                    |  |  .-------------------------.  |  |  |
                                    |  +--|-     Fluorescent       -|--|--+  |
                                    |  |  | )       Tube          ( |  |  |  |
                                    +--|--|-  (bipin or circline)  -|--|--|--+
                                    |  |  '-------------------------'  |  |  |
                                    |  |               +---------------+  |  |
                                    |  |      Grounded | Reflector        |  |
                                    |  |     ----------+----------        |  |
                                    |  |  .-------------------------.     |  |
                                    |  +--|-      Fluorescent      -|-----+  |
                                    |     | )        Tube         ( |        |
                   Line 2 (N) o-----+-----|-  (bipin or circline)  -|--------+
                                          '------------------------'
                      Note: The interlock normally present on most rapid/trigger 
                      start fixtures
                      have been removed to permit one lamp to operate if other 
                      is removed.
                      For preheat ballasts, wiring the filaments in parallel 
                      would probably result
                      in insufficient current to either lamp for it to start 
                      reliably. If the
                      filaments were wired in series, one lamp would probably 
                      start, but if the
                      filament of one lamp burned out or the lamp was removed, 
                      the fixture would
                      cease to function kind of defeating the purpose of these 
                      gyrations!
                      Wiring Fluorescent Lamps to Remote Ballasts
                      For reasonable distances, this should work reliably and be 
                      afe provided
                      that:
                        1. This is only attempted with iron ballasts. The fire 
                      safety and
                           reliability of electronic ballasts that are not in 
                      close proximity to
                           the lamps is unknown. The ballast may fail 
                      catastrophically either
                           immediately or a short time later as the circuit may 
                      depend on a low
                           impedance (physically short) path for stability.
                           In addition, there will almost certainly be 
                      substantial Radio Frequency
                           Interference (RFI) created by the high frequency 
                      currents in the long
                           wires. The FCC police (or your neighbors) will come 
                      and get you! This
                           may be a problem with iron ballasts as well - but 
                      probably of less
                           severity.
                        2. Wire of adequate rating is used. The starting voltage 
                      may exceed 1 kV.
                           Make sure the insulation is rated for at least twice 
                      this voltage. Use
                           18 AWG (or heavier) gauge wire.
                        3. There is no possibility of human contact either when 
                      operating or if
                           any connectors should accidentally come loose - 
                      dangerous line voltage
                           and high starting voltage will be present with tubes 
                      disconnected.
                      Note: one application that comes up for this type of 
                      remote setup is for
                      aquarium lighting. My recommendation would be to think 
                      twice about any
                      homebrew wiring around water. A GFCI may not help in terms 
                      of shock hazard
                      and/or may nuisance trip due to inductive nature of the 
                      ballast (both depend
                      at least in part on ballast design).
                      Wiring diagram of Low Power 220 VAC Fluorescent Lamp
                      (From: Manuel Kasper (mk@mediaklemm.com).)
                      The circuit in Low Power 220 VAC Fluorescent Lamp is from 
                      an AC line powered
                      'light stick'. So there's no fancy inverter circuit 
                      inside, but a simple
                      ballast without any nasty coils - just capacitors, 
                      resistors, and diodes. A
                      few modifications would probably be necessary to make it 
                      operate from 110
                      VAC. It runs the tube brighter than a similar lamp power 
                      from a 12 V
                      inverter. (See the section: "Automotive Light Stick 
                      Inverter" in the
                      document: Various Schematics and Diagrams. FWIW, the brand 
                      is
                      "Brennenstuhl".
                      It was damn hard to open up because everything was made 
                      out of thick plastic
                      with no screws (no wonder; it cost $6) - but thanks to a 
                      huge saw I managed
                      to get at the guts without destroying the tube or the 
                      circuit.
                        ------------------------------------------------------------------------
                      *Back to Sam's F-Lamp FAQ Table of Contents.
                      Specialty Fluorescent Lamp Types
                      All Sorts of Less Conventional Lamps
                      In addition to the boring white ones (OK, well 'white' 
                      does come in various
                                            colors!), other interesting types of 
                      lamps include all 
                      sorts of real colors
                      (red, green, blue, yellow), blacklight lamps, germicidal 
                      lamps in which
                      there is no phosphor coating at all and a quartz tube to 
                      transmit short-wave
                      UV light (e.g., EPROM erasers and PCB photoresist 
                      activation), sunlamps,
                      plant lights and special purpose specific wavelength lamps 
                      such as
                      reprography and copier lamps.
                      The basic technology is extremely flexible!
                      (From: Bruce Potter (s602531@aix2.uottawa.ca).)
                      There are also High Output and Very High Output types of 
                      lamps that have a
                      discharge current of 0.8 A and 1.5 A instead of the 
                      standard 0.3 A. HO and
                      VHO lamps are used when high light output is desired but 
                      are being outmoded
                      by HID lamps like metal halide.
                      Blacklight Fluorescent Lamps
                      (From: Don Klipstein (don@misty.com).)
                      BL in the tube designation (e.g., F40T12BL) means 
                      "blacklight", which is a
                      fluorescent lamp with a phosphor that emits the longest 
                      largely invisible UV
                      wavelengths that are both efficiently and fairly cheaply 
                      possible. This
                      phosphor seems to emit a band of UV mainly from 350 to 370 
                      nanometers, in
                      the UV-A range.
BLB                   means "blacklight-blue", differs from "blacklight" only i
                      glass tube of this lamp is darkly tinted with  with a dark
                      violet-blue color to absorb most visible light. Most UV 
                      gets through along with of dimly visible deep-violet 404.7
                      nanometer line of mercury. Most 
                      violetish-blue 435.8 nanometer line is absorbed, 
                      enough this wavelength gets through to dominate 
                      color of visible ligh .Longer visible light 
                      do not significantly penetrate BLB's 
                      very deep violet-blue glass, which is
                      known as 'Wood's glass'. UV is the same as that of  
                      BL lamp, being mostly between 350 and 370 nanometers.
                      There is a 350BL blacklight lamp, using a different 
                      phosphor that emits a band of slightly shorter UV 
                      in UV-A range. 
                      The reasoning for
                      this lamp is that it is supposedly optimized for 
                      attracting insects. These
                      lamps are one variety of UV lamps used in electric bug 
                      killers.
                      There are other UV fluorescent lamps. There are at least 
                      two different
                      UV/deep violet emitting fluorescent lamps used mainly in 
                      the graphic arts
                      industry, emitting mainly wavelengths between 360 and 420 
                      nanometers.
                      Possibly one of these is also used in bug killers. I have 
                      noticed one kind
                      of UV fluorescent lamp for bug killers with a broadish 
                      band phosphor with
                      significant output from the 360 nanometer range (maybe 
                      also shorter) into
                      visible wavelengths around 410 to 420 nanometers or so.
                      There is an even shorter UV-A lamp used for suntanning 
                      purposes. I would
                      guess the phosphor emits mainly within the 315 to 345 
                      nanometer range. One
                      brand of such lamps is "Uvalux".
                      There is even a UV-B emitting fluorescent lamp. Its 
                      phosphor emits mostly at
                      UV-B wavelengths (286 to 315 nanometers). It is used 
                      mainly for special
                      medicinal purposes. Exposing skin to UV-B causes erythema, 
                      which is to some
                      extent a burn reaction of the skin to a slightly 
                      destructive irritant. Use
                      of UV-B largely limits this to outer layers of the skin 
                      (perhaps mainly the
                      epidermis) and to parts of the body where skin is thinner. 
                      UV-A wavelengths
                      just over 315 nanometers can also cause sunburn, but they 
                      are more
                      penetrating and can affect the dermis. Please note that 
                      the deadliest
                      varieties of skin cancer usually originate in the 
                      epidermis and are usually
                      most easily caused by UV-B rays.
                      There are clear UV-emitting lamps made of a special glass 
                      that lets through
                      the main shortwave UV (UV-C) mercury radiation at 253.7 
                      nanometers. These
                      lamps are marketed as germicidal lamps, and ones in 
                      standard fluorescent
                      lamp sizes have part numbers that start with G instead of 
                      F. These lamps
                      will work in standard fluorescent lamp fixtures.
                      Cold-cathode germicidal lamps are also in use; these 
                      somewhat resemble
                      "neon" tubing.
                      Be warned that the shortwave UV emitted by germicidal 
                      lamps is intended to
                      be dangerous to living cells and is hazardous, especially 
                      to the conjunctiva
                      of eyes. Signs of injury by the UV are often delayed, 
                      often first becoming
                      apparent several minutes after exposure and peaking out a 
                      half hour to
                      several hours afterwards.
                      Please note that non-fluorescent (high pressure mercury 
                      vapor discharge)
                      sunlamps generally emit more UV-B rays rather than the 
                      tanning-range UV-A
                      rays. These lamps do have substantial UV-A output, but 
                      mainly at a small
                      cluster of wavelengths around 365 nanometers. Tanning is 
                      most effectively
                      accomplished by wavelengths in the 315-345 nanometer 
                      range. In addition, no
                      UV suntanning is completely safe.
                      Compact Fluorescent Lamps
                      These are miniaturized fluorescent lamps that usually have 
                      premium phosphors
                      which often come packaged with an integral ballast (either 
                      iron or
                      electronic). They typically have a standard screw base 
                      that can be installed
                      into nearly any table lamp or lighting fixture that 
                      accepts an incandescent
                      lamp.
                      Compact fluorescents are being heavily promoted as energy 
                      savings
                      alternatives to incandescent lamps. They also have a much 
                      longer life -
                      6,000 to 20,000 hours compared to 750 to 1000 hours for a 
                      standard
                      incandescent. While these basic premises are not in 
                      dispute - all is not
                      peaches and cream:
                        1. They are often physically larger than the 
                      incandescent bulbs they
                           replace and simply may not fit the lamp or fixture 
                      conveniently or at
                           all.
                        2. The funny elongated or circular shape may result in a 
                      less optimal
                           lighting pattern.
                        3. The light is generally cooler - less yellow - than 
                      incandescents - this
                           may be undesirable and result in less than pleasing 
                      contrast with
                           ordinary lamps and ceiling fixtures. Newer models 
                      have been addressing
                           this issue.
                        4. Some types (usually iron ballasts) may produce an 
                      annoying 120 Hz (or
                           100 Hz) flicker.
                        5. Ordinary dimmers cannot be used with compact 
                      fluorescents.
                        6. Like other fluorescents, operation at cold 
                      temperatures (under around
                           50-60 degrees F) may result in reduced light output. 
                      Starting may also
                           be erratic, although most compact fluorescent lamps 
                      seem to start OK at
                           temperatures near freezing. Many types start OK near 
                      zero degrees F.
                           Operation in an enclosed fixture often results in 
                      full light output in
                           cool surroundings after the lamp warms up for a few 
                      minutes, as long as
                           the initial temperature is high enough to permit a 
                      good start. However,
                           enclosing compact fluorescents often impairs their 
                      ability to work well
                           at higher temperatures.
                        7. There may be an audible buzz from the ballast.
                        8. They may produce Radio Frequency Interference (RFI).
                        9. The up-front cost is substantial (unless there is a 
                      large rebate): $10
                           to $20 for a compact fluorescent to replace a 60 W 
                      incandescent bulb!
                       10. Due to the high up-front cost, the pay-back period 
                      may approach
                           infinity.
                       11. While their life may be 20,000 hours, a wayward 
                      baseball will break one
                           of these $10 to $20 bulbs as easily as a 25 cent 
                      incandescent.
                      Nonetheless, due to the lower energy use and cooler 
                      operation, compact
                      fluorescents do represent a desirable alternative to 
                      incandescents. Just
                      don't open that investment account for all your increased 
                      savings just yet!
                      For more information, see the separate document on Compact 
                      Fluorescent
                      Lamps.
                      Cold Weather Fluorescent Lamps
                      (From: Bruce Potter (s602531@aix2.uottawa.ca).)
                      There are special lamps with heavy glass jackets and/or 
                      with krypton gas
                      filling for cold weather/freezer applications. They work 
                      best at below
                      room-temperatures. It really annoys me when I go to the 
                      grocery store or see
                      outside installations with dim, flickering tubes! What a 
                      waste of
                      electricity!
                        ------------------------------------------------------------------------
                           Blackened ends are somewhat reliable means 
                           of identifying bad tubes
                           in 34 or 40 watt rapid start fixtures. 
                           Failure of the electrodes/filaments at  ends 
                           result in either a low intensity glow or
                           flickering behavior, 
                      Premature Cathode Failure in Dimmed Fluorescent Lamps
                     there isn't enough
                      current flow to keep the cathodes warm a
                      is causing the discharge to
                      be concentrated on a small point. 
                      discharge will tend to stay on that
                      point since it's the only warm bit, 
                       and as such is emitting electrons,
                      making it the easiest path for current flow.
                      voltage drop across this point higher than normal 
                      since heat generated is  dissipated by rest of cathode  
                      means  more power than normal being dissipated from point
                      causing sputtering. causing the early burn-out.
cool white            which is a plain-old
                      white with a color like that of of average sunlight.
                      One bad thing about "cool white" 
                      spectrum  surplus of yellow and a shortage 
                      of green and red. 
Warm white            similar to incandescent lamps, although it slightly
                      less yellow and more white-pink. 
                      A warm white lamp's spectrum has a surplus
                      of yellow and violet-blue, 
                      and a shortage of red, green, and green-blue.
                      Like cool white, warm white can distort colors in 
common halophosphate  white is "white", which is between
                      "cool white" and "warm white" in color.
                      Other halophosphate whites, different shade 
                      of "warmth/coolness" include "supermarket white", "sign
                      white", "north light", "merchandising white", e
"natural".            has "cool white" halophosphate phosphor with a
                      red-glowing phosphor of a different type added in. 
                      lamps look slightly
                      pinkish in color, sometimes purplish when compared to  
                      warmer colored light
                      such as incandescent light. "Natural" fluorescent lamps 
                      make skin tones look pinkish, 
                      unlike usual halophosphate types which  skin tones look
                      green-yellowish. Some meat displays 
                      have "natural" fluorescent lamps to make
                      the meat look more red.
"triphosphor"         fluorescent lamps.  Triphosphor lamps 
                      come in various warm and cool shades,  designated
                      by "color temperature". This is  temperature 
                      that an ideal incandescent
                      radiator would be heated to in order to glow with a 
                      similar color. Color
                      codes on fluorescent lamps may include 
                      the color temperature or 1/100 of the color temperature. 
                      Osram/Sylvania brand lamps often have D8 immediately
                      preceding the color code.
                      2700 or 27 - orangish shade similar to incandescent lamps
                      3000 or 30 - "warm white", similar to whiter incandescent.
                      3500 or 35 - between warm white and cool white, 
                      similar to the whitest halogen lamps and projector lamps.
                      4100 or 41 - "cool white" or  color of average sunlight.
                      5000 or 50 - an icy cold pure white like t
                      hat of noontime tropical sunlight.
                      6500 or 65 - slightly bluish white or "daylight".
                      There are still other specialty whites, including ones 
usual failure         mode is depletion of emission mix on the filaments.
                      they do not emit electrons, and arc can't be sustained. 
                      Unless ballast supplies  high enough voltage 
                      that very high field can be set up
                      near the electrode. Then ions bombarding electrode 
                      have a high
                      enough energy to knock electrons out of  metal 
                      even with no emission mix,
                      or to heat the metal to the point it emits electrons. 
                      The high field is also
                      sufficient to ionize the argon fill gas---
                       normally only mercury is ionized.
                      The argon radiation is of a more purple color. That is  
                      probably what you
Blackening            at Ends of Fluorescent Tubes
                      themselves don't affect operation 
                      except to slightly reduce the
                      amount of light available since phosphor in that
                      area is dead. However,
                      they do represent loss of metal f
                      rom  electrodes (filaments).
                      cause is sputtering from filaments, 
                      mostly when cold. Thus. this
                      happens mostly when starting or 
                      with a defective rapid start ballast which
                      doesn't heat the filament(s) or a ballast 
                      or starter that continuously
                      cycles. When the filament is cold and is the cathode (on 
                      the negative half
                      of the AC cycle for that end of the tube), the work 
                      function is higher and
                      ions have a higher velocity when impacting, knocking off 
                      metal atoms in the
                      process. This is greatly reduced once the filament is up 
                      to normal operating
                      temperature (though even then, some sputtering is 
                      inevitable).
                      (From: Greg Grieves (ggrieves@home.com).)
                      Lamps with the longest lifetimes typically use the heavier 
                      noble gasses as
                      the buffer gas, ( Xenon or Krypton instead of Argon) 
                      because the sputtering
                      that occurs at the cathode is due to fast ion bombardment 
                      from the ionized
                      gasses in the tube. the heavier atoms have a smaller 
                      velocity for a given
                      kinetic energy of acceleration. its not the total energy 
                      of the ion that
                      sputters but its the momentum at impact that knocks other 
                      atoms loose. I
                      presume thats why Kr and Xe bulbs can run brighter, 
                      because they can crank
                      up the power and still have about the same lifetime. Some 
                      tubes use a
                      "hollow cathode" design in which the shape of the cathode 
                      is designed to
                      deflect impacting ions rather than be sputtered by them. 
                      That's my
                      understanding, anyway, theres much more to the story...
                      (From: PBerry1234 (pberry1234@aol.com).)
                      I recall one brand of lamp that positioned shields around 
                      the electrodes to
                      prevent the blackening. I suppose this improved the 
                      appearance in exposed
                      lamp applications, but don't know of any other benefits.
                      Hot Cathode Versus Cold Cathode Operation
                      The cathode is the negative electrode of a vacuum tube or 
                      gas filled
                      discharge tube. Current flows by way of electrons emitted 
                      from the cathode
                      and attracted to the positive electrode, the anode.
                      A hot cathode is one which must be heated to operate 
                      properly - to emit
                      sufficient electrons to be useful. Examples: TV and 
                      monitor CRTs, most
                      vacuum tubes (or valves), vacuum fluorescent displays 
                      (like those on your
                      VCR). This is called thermionic emission - the boiling off 
                      of electrons from
                      the surface of the cathode. Normal fluorescent lamps are 
                      hot cathode devices
                      - partially maintained by the discharge current itself. 
                      They all have some
                      sort of warmup period (though it can be quite short).
                      (From: Phil Rimmer (primmer@tunewell.com).)
                      A cold cathode is one where operation takes place without 
                      depending on
                      heating of the surface above ambient. There are all sorts 
                      of devices that
                      use 'cold' cathodes - neon lamps and signs, fluorescent 
                      backlight tubes, and
                      helium neon laser tubes. Naturally, cold cathode devices 
                      don't have much of
                      a warmup requirement.
                      The purpose of a cathode is to feed electrons into the 
                      negative end of the
                      positive column (the discharge) so they can variously 
                      excite and ionise gas
                      or vapour atoms.
                      Electrons are released from cathodes by the action of the 
                      positive ions
                      being accelerated towards them due to an electric field in 
                      the vicinity of
                      the cathode.
                      Electrons are broadly released in two ways: Thermal 
                      emission and secondary
                      emission.
                         * Thermal emission is the primary process used in "hot 
                      cathode" lamps
                           which include standard fluorescent tubes. The ions 
                      are accelerated
                           towards the cathode through a small cathode voltage 
                      (less than 10
                           volts) and gain just enough energy to heat a small 
                      part of the very
                           fine wire electrode when they collide with it. They 
                      heat it until it
                           glows dully and electrons are "boiled off", liberated 
                      by the thermal
                           energy. This process is very efficient in producing 
                      lots of electrons
                           and results in efficient lamps.
                         * Secondary emission is a more brutal process for 
                      generating electrons.
                           It requires an accelerating voltage drop of 130 to 
                      150 volts. It is
                           used in cold-cathode lamps that have relatively huge 
                      cylinders of iron
                           for electrodes. These massive electrodes require much 
                      too much energy
                           input to make them into thermal emitters. The 
                      energetic ions simply
                           "knock" electrons off the metal surface. In so doing 
                      they also knock
                           some of the metal off as well, a process called 
                      sputtering. The big
                           electrodes have enough material to last before other 
                      effects cause lamp
                           failure.
                      Hot cathode lamps operate in cold cathode mode if the 
                      cathode receives too
                      little energy to keep it glowing. The colliding ions are 
                      thirty times more
                      energetic than usual and soon sputter enough metal off the 
                      tiny electrodes
                      to destroy them.
                      Moral: Pre-heat the electrodes before starting the 
                      discharge and maintain
                      auxiliary current in the electrodes if the discharge 
                      current is low (e.g,
                      when dimming).
                      Comments on Small Inverter Powered Fluorescent Lamps
                      (From: Paul Bealing (paul@pmb.co.nz).)
                      Many small low cost inverters use a 2 transistor (one 
                      quite small) self
                      oscillating circuit. Simply minimum function, low cost. 
                      These circuits can
                      be quite efficient at low power levels. I have seen them 
                      used up to 50
                      watts.
                      Losses are usually in the transformer and the switching 
                      transistors. As the
                      currents increase, the losses usually increase for a given 
                      power output.
                      The lamp requires a high voltage, usually 300 to 500 V, to 
                      strike. The
                      voltage depends on the length/wattage of the lamp. Once 
                      struck, the current
                      through the lamp is limited to achieve the wattage. The 
                      voltage across a
                      small running lamp will be in the order of 60 to 100 volts 
                      AC.
                      Many simple inverters use a series resonant circuit to 
                      generate the high
                      strike voltage, which is disabled by the run current.
                      A couple of years ago I designed an inverter for a PL11 11 
                      Watt lamp based
                      on a switchmode power supply controller IC, 2 power 
                      mosfets, and a push-pull
                      transformer, running at about 200 kHz. The main 
                      application was in diesel
                      locomotives running from 75 V DC. I've had the circuit 
                      operating down to 10V
                      DC (different transformer winding). The primary current 
                      rises and the
                      dissipation increases.
                      Operating a Fluorescent Lamp on DC
                           "I have a application in mind that will use a DC 
                      power source
                           around 100 volts and fluorescent lighting. What kinds 
                      of voltage
                           do I need to sent the fluorescent? Are there any good 
                      sources of
                           info. for the circuitry I would need?"
                      (From: Don Klipstein (don@Misty.com).)
                      If it is a preheat tube of 22 watts or less, the 
                      cheap-and-dirty way to do
                      it is to use a normal preheat fixture. The only change is 
                      to add a resistor
                      in series with the ballast. This resistor should be maybe 
                      100 ohms for 20
                      and 22 watt lamps, slightly higher for lower wattage ones. 
                      It should be able
                      to safely dissipate a wattage comparable to that of the 
                      lamp.
                      The above includes most simple "PL"/twin-tube compact 
                      fluorescent lamps with
                      removable bulbs with two pins, as well as most compact 
                      fluorescent bulbs
                      with "choke" type ballasts running from 120 volts AC.
                      Should you need anything more energy-efficient than this, 
                      then there is the
                      world of electronic ballasts.
                      BTW, most low-power-factor screw-in 120 VAC compact 
                      fluorescent lamps with
                      electronic ballasts work fine "as-is" with about 160 volts 
                      DC or squarewave.
                      Ballasts and PCBs (The Hazmat Type)
                      (From: David Morris (allane@ix.netcom.com).)
                      Ballasts that were made after the late 70's do not contain 
                      PCB's. I spoke
                      with an Advance and GE ballast rep. a few years ago about 
                      this and I was
                      told the only sure-fire method to tell that there are no 
                      PCB's is if the
                      ballast says no PCB's. Any ballast that doesn't say that 
                      has a better than
                      80hance of having it. The amount in the ballast is VERY 
                      minute. Less than
                      a thimble full. It is used to cool a capacitor in the 
                      ballast. Since he said
                      the light is about 12 years old, I am quite certain that 
                      the ballast does
                      not contain PCB's. In our state, it is legal to dispose of 
                      these ballasts in
                      a limited quantity in your local landfill or throw them in 
                      the trash. Larger
                      quantities require Hazmat disposal methods. Our company 
                      policy is to leave
                      any old ballasts that is not marked 'no PCB's" with the 
                      customer for their
                      disposal.
                      As a side note, I read in one of the Electrical trade rags 
                      that the liquid
                      that replaced PCB's is testing out to be more dangerous 
                      than PCB's
                      themselves. Go figure!! :-)
                      As for catching fire, ballasts contain a thermal protector 
                      that will cut the
                      power if the ballast gets too hot. Only real old ballasts 
                      do not have this
                      feature. Ballasts marked Class P have this protection. It 
                      is very rare for
                      one of these ballasts to actually catch fire, although it 
                      does happen. More
                      often, they will smoke up the house if they overheat and 
                      the thermal
                      protector fails.
                      Driving Cold Cathode Fluorescent Lamps
                      (From: David VanHorn (dvanhorn@cedar.net).)
                      Linear Technology has several extremely detailed app notes 
                      written by Jim
                      Williams on this topic. It's more complicated than you 
                      might imagine to do
                      it right. Just making the tube light is perhaps only 10% 
                      of the job. The
                      rest includes keeping it running a long time without 
                      blackening, providing
                      the ability to set the brightness, not loosing all your 
                      energy to wiring
                      capacitance, and not creating an EMI nightmare.
                      Definitely read and understand those app notes, even if 
                      you go to another
                      vendor! The good news is that the actual circuit isn't 
                      that bad!
                      What is the E-Lamp?
                      The E-Lamp is one of those inventions that sounds like a 
                      really good idea
                      but still hasn't (as far as I know) made it into wide 
                      scale production. In
                      essence, it is an RF excited compact fluorescent lamp. 
                      Some of the E-lamp's
                      basic characteristics include.
                         * Fits into standard household light bulb bases.
                         * Radio frequency radiation was emitted, then converted 
                      to light.
                         * Dimmable using standard phase control dimmer - no 
                      special devices
                           needed.
                         * Very efficient so runs cool and consumes much less 
                      power than
                           incandescent lamps (don't know how it compares to 
                      compact
                           fluorescents).
                         * Desirable white spectral characteristics.
                         * No filament to wear out (and no wires through glass) 
                      so potentially
                           very long life.
                      Aside from cost issues, there could also be concerns with 
                      respect to RF
                      emissions effects on health and interference with other 
                      household appliances
                      and electronics.
                      (Victor Roberts (robertsv@ix.netcom.com).)
                      E-lamps are electrodeless fluorescent lamps. They use a 
                      high frequency or RF
                      magnetic field to create a time varying electric field 
                      which in turn drives
                      a discharge which is very similar to the discharge in an 
                      ordinary
                      fluorescent lamp. Except for the means by which the 
                      discharge is created,
                      these E-lamps and identical to all other fluorescent 
                      lamps. There is no
                      magic other than the fact that electrodeless excitation 
                      allows for the
                      elimination of the electrodes, so electrode failure and 
                      wear out are no
                      longer a problem. Also, electrodeless excitation removes 
                      the requirement
                      that the lamp be long and thin to achieve high efficacy. 
                      Proof of this is
                      beyond the scope of this note. :) Hence, an electrodeless 
                      fluorescent lamp
                      can be more easily made in the shape of an incandescent 
                      lamp.
                      There are also electrodeless metal halide lamps and, of 
                      course, the
                      electrodeless sulfur lamp.
fluorescent lamp      with colored glass spectrum INCLUDES mercury lines.  
                      strongest of these are the violet-blue one at 435.8 nm
                      and slightly yellowish green one at 546.1 nm. 
                      Weaker ones are the 404.7
                      and very weak 407.8 nm deep violet lines, 
                      very weak 491.6 and 496 nm blue-green lines, 
                      and the 577/579.1 nm yellow lines.
COLOR TEMPERATURE:    3000K -warm, comparable to incandescent  
                      slightly more orange or pink-orange and less yellow 
                      than incandescent. Includes  "Warm White".
                      3500K -whiter warm colo between 3000 and  4100 K.
                      4100K - plain white, including "cool white". 
                      About color of average sunlight.
                      5000K - icy cold pure white,
                      color of noontime tropical sunlight.
                      Sometimes looks slightly bluish.
                      6500K - bluish white, including "Daylight".
                      Note that these are more common color temperatures and 
                      there are others.
                      SPECTRAL/PHOSPHOR CLASS:
                      Halophosphate - these are the original types, which 
                      include "Warm White"
                      (3000K), "White" (3500K), "Cool White" (4100K) and 
                      "Daylight" (6500K). The
                      color rendering index (0-100 scale) is 53 for "Warm 
                      white", 62 for "Cool
                      white", and 79 for "Daylight". The spectrum is extra-rich 
                      in yellow and
                      orange-yellow and low on red and green. This causes reds 
                      and greens to look
                      darker and duller than normal and skin tones to be pale.
                      Deluxe Halophosphate / "broad spectrum" - These have 
                      improved color
                      rendering but with a compromise in light output.  color
                      distortions are
                      reduced compared to standard halophosphate lamps but 
                      although reduced in
                      degree they have the same characteristic. These lamps 
                      include "Deluxe Warm
                      White" (3000K), General Electric's "Merchandising White" 
                      (3500K), and
                      "Deluxe Cool White" (4100K with  color rendering index of 
                      89). There are
                      even further spectral improvements in this class, 
                      including General
                      Electric's "Soft White" (3000K) and their "Living White" 
                      (4100K with a color rendering index of 92).
                      Triphosphor - These lamps have a rare earth phosphor 
                      mixture. There are two
                      basic formulations which I refer to as "7" and "8". The 
                      "8" is the better
                      one and just about all compact fluorescent lamps use this 
                      formula. The color
                      rendering index is in the low to mid 80's. The spectrum 
                      has a strong
                      orange-red line at 611 nm, a strong narrow band with 
                      nearby narrow secondary
                      bands around 542 nm in the green, and a band in the 
                      blue-green. If the color
                      temperature is 3000K or higher, there is an additional 
                      broader band in the
                      blue. Osram/Sylvania lamps of this type have color codes 
                      D827 (2700K
                      compacts), D830 (3000K), D835 (3500K), D841 (4100K), and 
                      D850 (5000K).
                      General Electric lamps of this type have color codes 
                      SPX27, SPX30, SPX35,
                      SPX41, and SPX50. Philips lamps of this type include their 
                      "Advantage" and
                      "Ultralume" and "TL8" series - with part numbers including 
                      1/100 of the
                      color temperature.
                      Color distortions of this type of fluorescent lamp are 
                      different from those
                      of the halophosphate and deluxe halophosphate types. 
                      Greens and some reds
                      tend to be rendered brighter than normal. Skin tones look 
                      natural or
                      slightly more pink than normal. Some pure reds may be 
                      darkened but most
                      nearly pure reds such as red poinsettia leaves tend to be 
                      made slightly
                      orangish.
                      There is a "cheaper" triphosphor which I call the "7". 
                      This includes General
                      Electric SP (as opposed to SPX), Philips TL7 (as opposed 
                      to TL8), and
                      Osram/Sylvania's D7 (as opposed to D8). The color 
                      rendering index is in the
                      upper 70's. The main difference from the "8" phosphors is 
                      that the "7"
                      phosphors have a different green output that is more 
                      yellowish. This means
                      greens are not rendered as green as they would be rendered 
                      by the "8" types.
                      OFF-WHITE BASICALLY WHITE TYPES:
                      Natural - this is a "cool white" but with a 
                      deep-red-emitting ingredient
                      added to the phosphor. The color is a pinkish white that 
                      sometimes looks
                      purplish. Some meat display cases have these to make the 
                      meat look more red.
                      Some makeup mirrors with built-in fluorescent fixtures 
                      have these to make
                      skin tones look more pink.
                      Cool Green - this is an uncommon one that has a greenish 
                      white or
                      blue-greenish white color. It is brighter than "Daylight" 
                      but not quite as
                      bright as "cool white".
                      Colored, Specialty, Aquarium, Actinic, Plant-growing, 
                      Reptile, and
                      Ultraviolet Fluorescent Lamps
                      "*" preceding a specific brand/model/type indicates that I 
                      have actually
                      seen in person the spectrum of a working lamp of this 
                      type.
                      * "GREEN" (color code G) is a slightly whitish and very 
                      bright green.
                      The phosphor's spectral output is a broad band with a 
                      majority of the output
                      in the 505 to 570 nm range. This band extends visibly into 
                      the red.
                      * "BLUE" (color code B) is a whitish and very slightly 
                      greenish blue color.
                      The spectrum consists of a very broad band extending from 
                      approx. 410 nm in
                      the violet through approx. 540 nm in the green. This band 
                      extends
                      significantly into the red region, weakening gradually as 
                      wavelength
                      increases. With at least one of these lamps, I have seen a 
                      minor peak around
                      415 nm in the violet.
                      * "SPECIAL BLUE" (color code BB) This may be a Philips 
                      specialty. The
                      phosphor specializes in blue output - mostly between 420 
                      and 485 nm with a
                      majority between 425 and 475 nm and the peak is around 445 
                      nm. This lamp has
                      about 60 percent of the lumen light output of regular 
                      "blue" but it is at
                      least as eye-catching, maybe a little more.
                      This lamp has a medical application - treatment of 
                      hyperbilirubinemia, or
                      "yellow jaundice". In order to be good for this, the lamp 
                      output has to be
                      extremely low on UV output, and it surely accomplishes 
                      this. Either the
                      phosphopr or the glass has a UV block ingredient that even 
                      blocks at least
                      half of the 404.7 nm mercury line.
                      Aquarium Lamps:
                      Aquarium fluorescent lamps serve any of or any combination 
                      of three
                      functions:
                      1. Illuminate aquarium contents in a pleasing manner.
                      2. Provide light needed for plant growth.
                      3. Provide special (deep blue and/or violet blue) light 
                      needed by live
                      coral.
                      See below for more specific lamp types (actinic and 
                      plant-growth).
                      Actinic lamps - These lamps generally produce substantial 
                      violet,
                      violet-blue, and/or deep blue light needed by live coral. 
                      Some of these
                      lamps are also used for some photographic and 
                      photochemical industrial
                      processes.
                      * Hagen "MARINE-GLO" Visible Actinic - This is a very 
                      bright and vivid blue
                      fluorescent lamp intended for aquariums with live coral, 
                      which need
                      violet-blue and/or deep blue wavelengths of light. The 
                      color is less white
                      than the ordinary "blue" fluorescent lamp described above, 
                      but slightly
                      whiter and slightly greener than a computer monitor 
                      displaying a pure blue
                      screen. It looks at least as bright as a regular blue 
                      fluorescent lamp but
                      has a more-blue color that could be useful in signs.
                      The spectrum consists of a blue band and a green band 
                      which merge together
                      with hardly any dip in between. The blue band is stronger, 
                      with the green
                      band being just a little more than an extension of the 
                      blue band into the
                      green. I suspect the purpose of the green output is to 
                      give this lamp a
                      bright appearance or a not-too-low lumen rating - or to 
                      illuminate green
                      vegetation more pleasantly than a pure blue lamp would.
                      The strongest portion of the blue band is from 435 to 480 
                      nanometers, and
                      there is not much below 415 nm. The green band is mainly 
                      from 500 to 540 nm.
                      As noted above, the region between 480 and 500 nm is 
                      almost as strong as the
                      500 to 540 nm range. The green band extends weakly into 
                      the red region.
                      * Philips Actinic 03 or Super Actinic 03 (color code 03) - 
                      This lamp makes
                      mostly violet and violet-blue light. The color is a 
                      slightly dim and not
                      extremely deep violetish blue. I get an 
                      irritation/"pressure" sensation when
                      I look at this lamp directly at close range. I have seen 
                      this lamp sold for
                      illuminating aquariums with live coral, which require 
                      deep-blue and/or
                      violet-blue light. Although this lamp has a "blacklight" 
                      effect, this is due
                      to visible violet and not ultraviolet. I suspect this lamp 
                      is also used for
                      some photographic/photochemical industrial processes.
                      The phosphor band's spectrum seems basically confined to 
                      the 400 to 480 nM
                      range, with most of the output between 410 and 435 nm. The 
                      peak seems to be
                      in the 415 to 420 nm range (bluish violet). There is a 
                      very weak spectral
                      line around 610 nm in the red-orange.
                      Philips Actinic 05 - my knowledge of this one is mainly 
                      from the European
                      Philips online catalog, and it shows this lamp producing a 
                      broad band of
                      phosphor output throughout most of the UVA portion of 
                      ultraviolet and
                      through visible violet plus a bit of a "tail" throughout 
                      visible blue. The
                      broad phosphor band peaks around 365 nm. This is different 
                      rom blacklight
                      types which have a narrower band of phosphor output and 
                      usually also dark
                      violet glass tubing.
                      One application of the 05 Actinic is attracting insects 
                      since ones that are
                      attracted to light seem to like broadband light sources 
                      producing both blue
                      and UV.
                      * Coralife "100% Actinic 03 Blue 7100 K" - This lamp seems 
                      very similar to
                      the Philips actinic 03 in spectral output and color (I did 
                      not test both
                      _of_the_same_wattage_ side by side). The most significant 
                      difference between
                      these lamps was the presence of a very weak red-orange 
                      line near 610 nm in
                      the spectrum of the Philips lamp. This line was not 
                      present in the spectrum
                      of the Coralife lamp. This line accounts for only a 
                      fraction of 1 percent of
                      the output of the Philips lamp.
                      I don't know how Coralife thinks the color temperature is 
                      7100 Kelvin, or if
                      7100 K is just part of the name of the lamp and nothing to 
                      do with color
                      temperature. This lamp is much more blue than infinite 
                      color temperature.
                      Since this lamp is so similar to the Philips Actinic 03, 
                      get whichever costs
                      less.
                      * Coralife "50/50" (50% 6000 K, 50% actinic 03 blue 7100 
                      K) - I saw the
                      spectrum of one that may have been in use for quite a 
                      while, but found no
                      actinic blue content beyond that typical of a 
                      high-color-rendering-index
                      fluorescent lamp of this color (approx. 6500 Kelvin). The 
                      spectrum had the
                      611 nm (orange-red) and weaker orange and red lines of 
                      triphosphor red, the
                      542 nm narrow band of triphosphor green, and a broad band 
                      in the green and
                      blue (mostly 415 to 540 nm) like that of an ordinary blue 
                      fluorescent lamp.
                      * "AQUA" "Volt Arc" "Marine" - This lamp has a 
                      purple-white color close to
                      that of most plant-growing lamps, and is roughly as bright 
                      as many
                      plant-growing lamps, but is more of an actinic lamp. Use 
                      this lamp if you
                      like the color and color rendering effects and need an 
                      actinic lamp for live
                      coral. It is not as good at growing plants as other lamps 
                      of similar color,
                      and may be almost useless to any plants containing colored 
                      substances that
                      block blue and violet light.
                      The spectrum of this lamp has some red and green 
                      "triphosphor" spectral
                      content, namely the 611 nm orange-red line, weaker orange 
                      and red lines, and
                      the 542 nm narrow green band. The strongest phosphor 
                      spectrum feature is the
                      violet-blue band characteristic of actinic 03 lamps - from 
                      400 to 480 nm,
                      mostly 410 to 435, and peaking around 415-420.
                      * "Blue Moon" - This is basically a plain blue fluorescent 
                      lamp. The color
                      is slightly less green than that of a regular blue, and 
                      the spectrum has
                                            slightly less green and has a dim 
                      red-orange line near 610 nm that plain
                      blue fluorescent lamps don't have. Otherwise, the spectrum 
                      is close enough
                      to identical to that of an ordinary blue fluorescent lamp. 
                      In my opinion,
                      this lamp is minimally more beneficial to coral requiring 
                      actinic blue light
                      than a plain blue fluorescent lamp is.
                      * Duro-Test "Aquatinic" - This lamp is basically a
                      high-color-rendering-index, largely triphosphor 6500 
                      Kelvin lamp. Its
                      spectrum is basically triphosphor, with the orange-red 
                      line around 611 nm,
                      the dimmer orange and red lines, the green one near 542 
                      nm, and the
                      blue-green band around 480-495 nm. The blue-green band has 
                      a slightly
                      different shape than usual for triphosphor lamps. There is 
                      a somewhat dim,
                      broad band throughout the blue and green range (mostly 
                      415-540 nm),
                      resembling the phosphor output of a regular blue 
                      fluorescent lamp. This is
                      instead of the 440-475 nm band normally present in the 
                      spectrum of
                      triphosphor lamps with color temperatures 3500 Kelvin and 
                      higher.
                      This lamp probably has a slightly higher color rendering 
                      index and slightly
                      better scotopic vision stimulation than that of most 
                      triphosphor lamps of
                      similar color temperature. In my judgement, its actinic 
                      benefit to coral is
                      hardly to not at all more than that of most triphosphor 
                      lamps of color
                      temperature 5,000 Kelvin or higher. I believe it is 
                      mis-named and
                      overpriced.
                      Plant Growing Lamps: (Aquarium or otherwise)
                      The usual plant photosynthesis using chlorophyl works best 
                      from red light.
                      There are two slightly distinct processes that both work 
                      best from red
                      light. Both work well from red wavelengths from 610 to 675 
                      nm, and one of
                      them also efficiently utilizes wavelengths up to 695 nm. 
plant_fluorescent     for growth purposes usually produce most of their spectral
                      output in the 630 to 670 nm range. These wavelengths are 
                      red, and not as visible as shorter red wavelengths in 
                      610 to 630 nm range typical of fluorescent lamps 
                      designed for maximum apparantly visible red output.
                      Therefore, plant-growing lamps are not as bright 
                      they usually have a light purple color noticeably dimmer
                      chlorophyl also utilizes blue light, not as well as red
                      photosensitive chemicals such as carotene
                      respond to deep blue and violet-blue light,  
                      some plants may need some blue light for proper health.
                      plants will usually get enough from violet-blue 435.8 nm 
                      mercury line from any fluorescent lamps 

                      that provide enough red light. Use of 
                      blue light by
                      chlorophyl may be impaired in a few types of plants by 
                      colored substances in
                      these plants that block blue light.
                      Plants will utilize orange and orange-yellow light, just 
                      not quite as
                      effectively as red light. Fluorescent lamps rich in orange 
                      and orange-yellow
                      output will generally work, but you may need enough 
                      lighting to be
                      distractingly bright since human eyes are more sensitive 
                      to orange and
                      yellow light than to the deep red wavelengths that plant 
                      lights are
                      optimized to produce.
                      Please note that lowest-color-temperature ("warmest") 
                      tri-phosphor lamps
                      (generally with rated color temperature at or near 3,000 
                      Kelvin) produce
                      lots of orangish red light around 611 nm, and will grow 
                      plants somewhat
                      better than other white and near-white fluorescent lamps. 
                      These will grow
                      plants almost as well as lights made for plants, but will 
                      look brighter.
                      Lights optimized for plant growth are low on green output, 
                      since plants
                      reflect green light and cannot utilize green light. One 
                      side effect is
                      making red and blue objects look extra bright, and making 
                      green objects look
                      an extra-deep darker shade of green. Part of the 
                      color-enhancing effect is
                      from a relative lack of orange, yellow, and blue-green 
                      wavelengths that make
                      green objects look slightly less green, with the presence 
                      of some nearly
                      pure (only slightly yellowish) green light from the 546.1 
                      nm mercury line.
                      The shortage of orange and yellow light results in red 
                      objects looking vivid
                      pure red. All this results in a general color-enhancing 
                      effect which is
                      often considered a desirable side effect of plant-growing 
                      fluorescent lamps.
                      * "Aquarilux" "Aquarium Light" - This is a common model of 
                      fluorescent lamp
                      nearly optimized for growing plants. The phosphor spectrum 
                      consists mainly
                      of a 5-peak red band, with the major peaks near 624, 632, 
                      648, and 660 nm.
                      Within each of these two pairs, the longer wavelength peak 
                      is somewhat
                      stronger. The 648-660 pair is substantially stronger than 
                      the 624-632 nm
                      pair, but looks slightly dimmer due to the lower 
                      visibility of the longer
                      wavelengths. There is a much weaker peak in the middle 
                      near 640 nm.
                      In addition to the strong 5-peak red band, there is a weak 
                      continuous
                      spectrum.
                      Reptile Lamps such as "Day Cycle" and "Repti-Sun 2.0" - 
                      These are lamps with
                      a cooler white color with a color temperature in the 5000 
                      to 6500 Kelvin
                      range and a high color rendering index, as well as 
                      ultraviolet-emitting
                      phosphors. There is UVA output as well as UVB output. The 
                      UVB content is
                      usually 2 to 2.4 percent of the total output. Please note 
                      that the
                      UVB/visible ratio is about 2-3 times that of average 
                      noontime tropical
                      sunlight, so your illumination should generally not exceed 
                      1/3 that of
                      tropical sunlight. Otherwise, the spectral content roughly 
                      simulates
                      tropical daylight.
                      Since average high-noon tropical sunlight is approx. 500 
                      watts of visible
                      and UV per square meter and these lamps are approx. 25 
                      percent efficient at
                      producing this, between 500 and 1,000 watts (lamp wattage) 
                      per square meter,
                      or 45 to 95 watts per square foot, will give roughly as 
                      much UVB as
                      high-noon tropical sunlight. I doubt most life forms want 
                      full-blast
                      noontime UVB all day, so you probably want less. For 
                      better info, consult
                      herpetology experts who know the needs of your specific 
                      pets. Please also
                      note that human skin generally does not want much UVB, and 
                      human eyes like
                      it even less.
                      There are "Repti-Sun 5.0" and "Iguana Light 5.0" lamps. 
                      These are of the
                      same brand ("Zoo-Med") and are identical in all 
                      specifications printed on
                      the package. I am guessing that they may or may not be 
                      different - possibly
                      the Repti-Sun is more of a broad-spectrum type and the 
                      Iguana Light may be
                      more triphosphor. (?) Both of these lamps have 5 percent 
                      of their total
                      output in the UVB range, slightly over twice that of other 
                      reptile lamps.
                      * Blacklight (color code BL) - This fluorescent lamp has a 
                      phosphor emitting
                      UV, mostly near 360 nm. This is the non-filtered type of 
                      blacklight. It
                      glows light blue.
                      * Blacklight Blue (color code BLB) - This is the filtered 
                      type of
                      blacklight. The tubing is made of dark violet, 
                      UV-transparant glass known as
                      Wood's Glass. The color is a very dim and very deep 
                      violet-blue. The UV
                      output and the deep violet 404.7 nM mercury line get 
                      through easily. The
                      violet-blue 435.8 nm mercury line is significantly 
                      attenuated, but enough
                      gets through for this wavelength to dominate the color of 
                      the visible light
                      from this lamp. All longer visible wavelengths 
                      significantly emitted from
                      inside the lamp are very highly blocked by the dark violet 
                      glass.
                      * 350BL - This is an unfiltered blacklight similar to the 
                      BL, except that a
                      different phosphor emitting mostly ultraviolet wavelengths 
                      near 350 nm is
                      used. This phosphor's spectral band has a slight tail that 
                      extends
                      detectably to approx. 420 nm in the visible violet.
                      350 BL lamps are often used in electric bug killers, since 
                      the 350 nm range
                      of UV is supposedly more attractive to insects than the 
                      360 nm range. I
                      think the advantge of the 350 over the 360 is in the wider 
                      bandwidth of the
                      350 - I have done a few experiments that give me some 
                      indication that
                      insects are better attracted by light sources of wider 
                      bandwidth, preferably
                      stimulating both the "UV" and the "blue" of the four types 
                      of color sensors
                      in insect eyes.
                      ------------
                      This is a collection of non-intelligent (at least for now) 
                      inverter circuits
                      for operating fluorescent or other similar devices from 
                      low voltage DC power
                      sources.  These designs - mostly obtained by reverse 
                      engineering commercial
                      camping lanterns, power inverters, and the like - are all 
                      very basic circuits
                      which use simple oscillators, easy to obtain or construct 
                      transformers, and
                      common power semiconductors.
                      These designs can easily be modified for other purposes 
                      such as powering
                      photoflash or signal strobes and HeNe lasers.
                      Additional circuits will be added as they become 
                      available.  Contributions
                      are welcome.
                      Super simple inverter:
                      ---------------------
                      This circuit can be used to power a small strobe or 
                      fluorescent lamp.  It will
                      generate over 400 VDC from a 12 VDC, 2.5 A power supply or 
                      an auto or marine
                      battery.  While size, weight, and efficiency are nothing 
                      to write home about -
                      in fact, they are quite pitiful - all components are 
                      readily available (even
                      from Radio Shack) and construction is very 
                      straightforward.  No custom coils
                      or transformers are required.  If wired correctly, it will 
                      work.
                      Output depends on input voltage.  Adjust for your 
                      application.  With the
                      component values given, it will generate over 400 V from a 
                      12 V supply and
                      charge a 200 uF capacitor to 300 V in under 5 seconds.
                      For your less intense applications, a fluorescent lamp can 
                      be powered directly
                      from the secondary (without any other components).  This 
                      works reasonably well
                      with a T5-13W or T8-15W bulb but Q1 does get quite hot so 
                      use a good heat sink.