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  1. Fluorescent Lighting document - long
    by ptimlin/ (patrick timlin) (19 Sep 1997)

Fluorescent Lighting document - long

by ptimlin/ (patrick timlin)
Date: 19 Sep 1997

   *        Fluorescent Light Bulbs, Lamps, and Lighting Fixtures         *
   *                                                                      *
   *                       **** Version 1.72 ****                         *
   *                                                                      *
   *                       Copyright (C) 1996,1997                        *
   *                        Samuel M. Goldwasser                          *
   *                        Donald L. Klipstein                           *
   *                                                                      *
   *        Corrections or suggestions to:        *
   *                                               *
   *                                                                      *
   *                     --- All Rights Reserved ---                      *
   *                                                                      *
   *    Reproduction of this document in whole or in part is permitted    *
   *    if both of the following conditions are satisfied:                *
   *                                                                      *
   *     1. This notice is included in its entirety at the beginning.     *
   *     2. There is no charge except to cover the costs of copying.      *
   *                                                                      *

             ****************  Introduction  ****************

Fluorescent lamp basics:

The fluorescent lamp was the first major advance to be a commercial success
in small scale lighting since the tungsten incandescent bulb.  Its greatly
increased efficiency resulted in cool (temperature wise) brightly lit
workplaces (offices and factories) as well as home kitchens and baths.
The development of the mercury vapor high intensity discharge (HID) lamp
actually predates the fluorescent (the latter being introduced commercially
in 1938, four years after the HID).  However, HID type lamps have only
relatively recently become popular in small sizes for task lighting in
the home and office; yard and security area lighting; and light source
applications in overhead, computer, and video projectors.

Fluorescent lamps are a type of gas discharge tube similar to neon signs
and mercury or sodium vapor street or yard lights.  A pair of electrodes,
one at each end - are sealed along with a drop of mercury and some inert
gases (usually argon) at very low pressure inside a glass tube.  The
inside of the tube is coated with a phosphor which produces visible light
when excited with ultra-violet (UV) radiation.  The electrodes are in the
form of filaments which for preheat and rapid or warm start fixtures are
heated during the starting process to decrease the voltage requirements
and remain hot during normal operation as a result of the gas discharge
(bombardment by positive ions).

When the lamp is off, the mercury/gas mixture is non-conductive.  When power
is first applied, a high voltage (several hundred volts) is needed to 
the discharge.  However, once this takes place, a much lower voltage -
usually under 100 V for tubes under 30 watts, 100 to 175 volts for 30
watts or more - is needed to maintain it.

The electric current passing through the low pressure gases emits quite a
bit of UV (but not much visible light).  The gas discharge's radiation is
almost entirely mercury radiation, although the gas mixture is mostly
inert gas and generally around something like 1 percent mercury vapor.
The internal phosphor coating very efficiently converts most of the UV to
visible light.  The mix of the phosphor(s) is used to tailor the light
spectrum to the intended application.  Thus, there are cool white, warm
white, colored, and black light fluorescent (long wave UV) lamps.  There
are also lamps intended for medical or industrial uses with a special
envelope such as quartz that passes short wave UV radiation.  Some
have an uncoated envelope, and emit short-wave UV mercury radiation.
Others have phosphors that convert shortwave UV to medium wave UV.

(Caution: many of these emit shortwave or medium wave UV which is
harmful and should not be used without appropriate protection in an
enclosure which prevents the escape of harmful UV radiation.) 

Fluorescent lamps are about 2-4 times as efficient as incandescent lamps
at producing light at the wavelengths that are useful to humans.  Thus,
they run cooler for the same effective light output.  The bulbs themselves
also last a lot longer - 10,000 to 20,000 hours vs. 1000 hours for a typical
incandescent.  However, for certain types of ballasts, this is only achieved
if the fluorescent lamp is left on for long periods of time without frequent
on-off cycles.

Fluorescent lamp labeling:

The actual fluorescent tubes are identified by several letters and numbers
and will look something like 'F40CW-T12' or 'FC12-T10'.

So, the typical labeling is of the form FSWWCCC-TDD (variations on this
format are possible):

F  -  Fluorescent lamp.  G means Germicidal shortwave UV lamp.
S  -  Style - no letter indicates normal straight tube; C for Circline.
WW -  Nominal power in Watts.  4, 5, 8, 12, 15, 20, 30, 40, etc.
CCC - Color.  W=White, CW=Cool white, WW=Warm white, BL/BLB=Black light, etc.
T  -  Tubular bulb.
DD -  Diameter of tube in of eighths of an inch.  T8 is 1", T12 is 1.5", etc.

For the most common T12 (1.5 inch) tube, the wattage (except for newer
energy saving types) is usually 5/6 of the length in inches.  Thus, an
F40-T12 tube is 48 inches long.

     ***************  Fluorescent Fixtures and Ballasts  ****************

Fluorescent fixtures:

The typical fixture consists of:

* Lamp holder - the most common is designed for the straight bipin base bulb.
  The 12, 15, 24, and 48 inch straight fixtures are common in household and
  office use.  The 4 foot (48") type is probably the most widely used size.
  U shaped, circular (Circline(tm)), and other specialty tubes are also

* Ballast(s) - these are available for either 1 or 2 lamps.  Fixtures with
  4 lamps usually have two ballasts.  See the sections below on ballasts.
  The ballast performs two functions: current limiting and providing the
  starting kick to ionize the gas in the fluorescent tube(s).

* Switch - on/off control unless connected directly to building wiring in
  which case there will be a switch or relay elsewhere.  The power switch
  may have a momentary 'start' position if there is no starter and the
  ballast does not provide this function.

* Starter (preheat fixtures only) - device to initiate the electrode
  preheating and high voltage "kick" needed for starting.  In other
  fixture types, the ballast handles this function. 

Fluorescent Lamp Ballasts:

For a detailed explanation, check your library.  Here is a brief summary.

A ballast serves two functions:

1. Provide the starting kick.
2. Limit the current to the proper value for the tube you are using.

In the old days fluorescent fixtures had a starter or a power switch with
a 'start' position which is in essence a manual starter.  Some cheap ones
still do use this technology.

The starter is a time delay switch which when first powered, allows the
filaments at each end of the tube to warm up and then interrupts this part
of the circuit.  The inductive kick as a result of interrupting the current
through the inductive ballast provides enough voltage to ionize the gas
mixture in the tube and then the current through the tube keeps the
filaments hot - usually.  You will notice that a few iterations are sometimes
needed to get the tube to light.  The starter may keep cycling indefinitely
if either it or one of the tubes is faulty.  While the lamp is on, a
preheat ballast is just an inductor which at 60 Hz (or 50 Hz) has the
appropriate impedance to limit the current to the tube(s) to the proper 

Ballasts must generally be fairly closely matched to the lamp in terms
tube wattage, length, and diameter.

Types of iron ballasts:

Instant start, trigger start, rapid start, etc. ballasts include loosely
coupled high voltage windings and other stuff and do away with the starter:

1. The ballast for a preheat fixture (combined with a starter or power
   switch with a 'start' position) is basically a series inductor. 
   Interrupting current through the inductor provides the starting voltage.

2. The ballast for an instant start fixture has a loosely coupled high
   voltage transformer winding providing about 500-600 V for starting
   in addition to the series inductor.  The electrodes of "instant start"
   bulbs are designed for starting without preheating.

3. The ballast for a rapid start fixture has in addition small windings for
   heating the filaments reducing the required starting voltage to 
250-400 V.
   Trigger start fixtures are similar to rapid start fixtures.

Starting voltage is either provided by the inductive kick upon interruption
of the current bypassed through the starter for (1) or a high voltage winding
in (2) and (3).

In all cases, the current limiting is provided primarily by the impedance
of the series inductance at 60 Hz (or 50 Hz depending on where you live).

Electronic ballasts:

These devices are basically switching power supplies that eliminate the
large, heavy, 'iron' ballast and replace it with an integrated high frequency
inverter/switcher.  Current limiting is then done by a very small 
inductor, which has sufficient impedance at the high frequency.  Properly
designed electronic ballasts should be very reliable.  Whether they actual
are reliable in practice depends on their location with respect to the heat
produced by the lamps as well as many other factors.  Since these ballasts
include rectification, filtering, and operate the tubes at a high frequency,
they also usually eliminate or greatly reduce the 100/120 Hz flicker
associated with iron ballasted systems.

I have heard, however, of problems with these relating to radio frequency
interference from the ballasts and tubes.  Other complaints have resulted
due to erratic behavior of electronic equipment using infra red remote

There is a small amount of IR emission from the fluorescent tubes themselves
and this ends up being pulsed at the inverter frequencies which are
sometimes similar to those used by IR hand held remote controls.

Some electronic ballasts draw odd current waveforms with high peak
currents.  This is due to the fact that these ballasts (low-power-factor
type) have a full-wave-bridge rectifier and a filter capacitor.  Current
can only be drawn during the brief times that the instantaneous line
voltage exceeds the filter capacitor voltage.

Because of the high peak currents drawn by some electronic ballasts, it is
often important to size wiring properly for these high peak currents.  For
wiring heating and fuse/circuit considerations, one should allow for a
current of 4 to 6 times the ratio of lamp watts to line volts.  For wiring
voltage drop considerations (drop in voltage the ballast's filter capacitor
gets charged to), the effective current is even higher, sometimes as high
as 15 to 20 times the ratio of the lamp watts to RMS line volts.

For less than 50 watts, the current drawn by low-power-factor electronic
ballasts is usually not a problem.  For multiple ballasts or total
wattages over 50 watts, it may be important to consider the effective
current drawn by low-power-factor electronic ballasts.

If you want to get an idea of some typical modern electronic ballast designs,
see the International Rectifier web site.  Search for 'electronic ballasts'
or download the following reference design notes:

* (Linear Ballast)
* (Compact Ballast)

    ****************  Fluorescent Fixture Wiring Diagrams  ***************

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    |

Here is a variation that some preheat ballasts use.  This type was found on
a F13-T5 lamp fixture. Similar types are used for 30 and 40 watt preheat
lamps. This 3-lead preheat ballast is a voltage-boosting "high leakage
reactance autotransformer" used if the voltage across the tube is much
over approx. 60 percent of the line voltage. For technical details on why a
fluorescent lamp will not work with ordinary ballasts if the tube voltage is
only slightly less than the line voltage, look at Don Klipstein's
Discharge Lamp Mechanics document.

              Power Switch   +-------------+
 Line 1 (H) o------/ --------|A  Ballast   |
                  +----------|B           C|----------+
                  |          +-------------+          |
                  |                                   |
                  |   .--------------------------.    |
 Line 2 (N) o-----+---|-       Fluorescent      -|----+
                      | )         Tube         ( |
                  +---|-         (bipin)        -|----+
                  |   '--------------------------'    |
                  |                                   |
                  |          +-------------+          |  
                  |          |   Starter   |          |
                  +----------| or starting |----------+
                             |   switch    |

Fluorescent starter operation:

The starter 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 extinguished, 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. 

Where a manual starting switch is used instead of an automatic starter,
there will be three switch positions:

OFF:   Both switches are open.
ON:    Power switch is closed.
START: (momentary) Power switch remains closed and starting switch in 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 circ.)  -|-------+ 

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

             Power Switch    +--------------------------+
 Line 1 (H) o----/ ----------|Black    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 
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               (5) )|| Filament 1
              Red o----------------------+---+ ||
                                         |     ||
                                         +     ||
                                          )||==|| Stepup winding/choke is
                     82.5 V          (37) )||  || loosely coupled to main
                                          )||==|| magnetic circuit
                                         +     ||
                                         |     ||
   +--> Black (H) o----------------------+---+ ||
   |                                          )|| Primary of starting
                    106.5 V              (31) )|| autotransformer
 115 V                                        )||
             Blue o--------------------------+ ||
   |                  8.5 V               (3) )|| Filament 2
   +--> 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)


    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


  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

Wiring fluorescent lamps to remote ballasts:

For reasonable distances, this should work reliably and be safe provided 

1. This is only attempted with iron ballasts.  The fire safety and 
   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

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 
   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).

      ****************  Special Fluorescent Lamp Types  ****************

Fluorescent black light bulbs:

(From: Don Klipstein (

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", which differs from "blacklight" only in that
the glass tube of this lamp is darkly tinted with something with a dark
violet-blue color to absorb most visible light.  Most UV gets through
this, along with much of the dimly visible deep-violet 404.7 nanometer
line of mercury.  Most of the violetish-blue 435.8 nanometer line is
absorbed, but enough of this wavelength gets through to largely dominate
the color of the visible light from this lamp.  Longer visible light
wavelengths do not significantly penetrate the BLB's very deep violet-blue
glass, which is known as 'Wood's glass'.  The UV is the same as that of
the 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 wavelengths in the 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

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 410-420 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 
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 
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 
    lamps and ceiling fixtures.  Newer models have been addressing this 

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 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.

    ****************  Troubleshooting OF Fluorescent Lamps  **************

Problems with fluorescent lamps and fixtures:

In addition to the usual defective or damaged plugs, broken wires in the
cord, general bad connections, fluorescent lamps and fixtures have some
unique problems of their own.  The following assumes a lamp or fixture
with a conventional iron (non-electronic) ballast.  Always try a new set
of fluorescent tubes and starter (where used) before considering other
possible failures.
If two tubes dim or flicker in unison, this means that both are powered
by the same ballast.  Often this means that one tube has failed, although
the other tube may also be in poor condition or approaching the end of its
life.  Both tubes must be replaced with known good tubes in order to rule
out a defective ballast.

1. Bad fluorescent tubes.  Unlike incandescent lamps where a visual 
   of the bulb itself will often identify a broken filament, there is often
   no way of just looking at a fluorescent tube to determine if it is bad.
   It may look perfectly ok though burned out fluorescents will often have
   one or both ends blackened.  However, a blackened end is not in itself
   always an indication of a bad tube.  Blackened ends are a somewhat
   reliable means of identifying bad tubes in 34 or 40 watt rapid start
   fixtures.  Blackened ends are not as reliable an indicator in preheat
   or trigger start fixtures, or for tubes of 20 watts or less.

   Failure of the electrodes/filaments at one or both ends of the the
   fluorescent tube will usually result in either a low intensity glow or
   flickering behavior, or sometimes in no light at all.  A broken
   filament in a fluorescent tube used in a preheat type fixture (with a
   starter) will almost always result in a totally dead lamp as there will
   be no power to the starter.  Dim glow is rare in this case and would
   probably be confined to the region of the broken filament if it occurs.
   The best approach is to simply try replacing any suspect tubes -
   preferably both in a pair that are driven from a single ballast.

   In fixtures where a rapid start ballast runs two tubes, both tubes will
   go out when one fails.  Sometimes one or both tubes will glow dimly
   and/or flicker.  If one tube glows dimly and the other is completely
   dead, this does not indicate which tube has failed.  The brighter tube
   may be the good one or the bad one.  The bad tube usually has noticeable
   blackening at one end.  It may pay to replace both tubes, especially if
   significant labor costs are involved.  Also, prolonged dim-glowing may
   degrade the tube that did not initially fail.

   In trigger start fixtures that use one ballast to power two 20 watt
   tubes, sometimes both tubes will blink or intermittently dim.
   Replacing either tube with a known good tube may fail to fix this.  The
   tubes may continue blinking or intermittently dimming until both are
   replaced with brand new tubes.  This sometimes indicates borderline low
   line voltage ("brownout", etc.), nonideal temperatures, or a borderline
   (probably cheaply designed) ballast.

2. Bad starter (preheat fixtures only).  The little starter can may go bad
   or be damaged by faulty fluorescent tubes continuously trying to start
   unsuccessfully.  It is a good idea to replace the starter whenever tubes
   are replaced in these types of fixtures.  One way that starters go bad is
   to "get stuck".  Symptoms of this are the ends of the affected tube
   glowing, usually with an orange color of some sort or another but
   sometimes with a color closer to the tube's normal color if arcs form
   across the filaments.  Occaisionally, only one end arcs and glows 
   brightly, and the other end glows dimmer with a more orange color.

   Please note that this is hard on both the tube and the ballast, and the
   defective starter should be immediately removed.

   Should one or both ends glow with a bright yellowish orange color with
   no sign of any arc discharge surrounding each filament, then the emissive
   material on the filaments is probably depleted or defective. In such a
   case, the tube should be replaced regardless of what else is wrong.

3. Defective iron ballast.  The ballast may be obviously burned and smelly,
   overheated, or have a loud hum or buzz.  Eventually, a thermal protector
   built into many ballasts will open due to the overheating (though this 
   probably reset when it cools down).  The fixture may appear to be dead.
   A bad ballast could conceivably damage other parts as well and blow the
   fluorescent tubes.  If the high voltage windings of rapid start or trigger
   start ballasts are open or shorted, then the lamp will not start.

   Ballasts for fixtures less than 30 watts usually do not have thermal
   protection and in rare cases catch fire if they overheat.  Defective
   fixtures should not be left operating.

4. Bad sockets.  These can be damaged through forceful installation or
   removal of a fluorescent tube.  With some ballasts (instant start,
   for example), a switch contact in the socket prevents generation of the
   starting voltage if there is no tube in place.  This minimizes the
   possibility of shock while changing tubes but can also be an additional
   spot for a faulty connection.

5. Lack of ground.  For fluorescent fixtures using rapid start or instant
   start ballasts, it is often necessary for the metal reflector to be
   connected to the electrical system's safety ground.  If this is not
   done, starting may be erratic or may require you to run your hand over
   the tube to get it to light.  In addition, of course, it is an important
   safety requirement.

Warning: electronic ballasts are switching power supplies and need to be
serviced by someone qualified in their repair both for personal safety as
well as continued protection from electrical and fire hazards.

Why do fluorescent lamps buzz and what to do about it?

The buzzing light is probably a mundane problem with a defective or cheap
ballast.  There's also the possibility of sloppy mechanical construction
which lets something vibrate from the magnetic field of the ballast until
thermal expansion eventually stops it.

First check for loose or vibrating sheetmetal parts - the ballast may
simply be vibrating these and itself not be defective.

Most newer fixtures are of the 'rapid start' or 'warm start' variety and
do not have starters.  The ballast has a high voltage winding which provides
the starting voltage.

There will always be a ballast - it is necessary to limit the current to the
tube(s) and for starting if there is no starter.  In older fixtures, 
these will
be big heavy magnetic choke/transformer devices - hard to miss if you
open the thing.  Cheap and/or defective ones tend to make noise.  They
are replaceable but you need to get one of the same type and ratings -
hopefully of higher quality.  A new fixture may be cheaper.

The starter if present is a small cylindrical aluminum can, approximately
3/4" x 1-1/2" in a socket, usually accessible without disassembly.  It
twists counterclockwise to remove.  They are inexpensive but probably not
your problem.  To verify, simply remove the starter after the lamp is on 
- it
is not needed then.

The newest fixtures may use totally electronic ballasts which are less
likely to buzz.  Warning: electronic ballasts are basically switching
power supplies and are maybe hazardous to service (both in terms of
your safety and the risk of a fire hazard from improper repair) unless
you have the appropriate knowledge and experience.

Replacement ballast buzzes:

Assuming the replacement is of the same type as the original and it is 
mounted, there is probably nothing really wrong - it is just not as quiet as
your previous ballast.  Make sure it is the ballast and not its mounting 
metal vibrating.  If the sound is coming from the ballast, there really isn't
a lot that can be done other than to try another manufacturer or sample.  
see the section: "Why do fluorescent lamps buzz and what to do about it?".

(From Brian Beck (

There are 2 main types of ballasts; those for 'home' use and those for
commercial use.  The commercial type will last longer and the lamp life
is better as well.

There are three sound ratings:

* A - extremely quiet (e.g., libraries, churches).
* B - somewhat noisy (e.g., work areas, shops).
* C - outdoor noisy (e.g., 60 foot poles in parking lots).

My guess is you got a home rated ballast with a 'B' sound rating.  There
is nothing wrong with the ballast - it is just noisy.  If the buzz bothers
you, return it to the store you bought it and go purchase one at an actual
electrical parts supplier (home centers and hardware stores may not have
the highest quality components).  For a 2 lamp F40/T12/CW/SS lamp fixture,
you want an R2S40TP ballast.

Why fluorescent lamps may not be as bright as you thought?:

"I recently replaced a kitchen overhead fixture with two 75 watt bulbs
 with a fluorescent one having two 20 W bulbs. Guess what? Not enough light!"

 Somehow I was under the impression that a watt of fluorescent lighting
 produced many more candles than a watt of incandescent lighting, but
 obviously, I overestimated the ratio."

A 20 watt fluorescent bulb of a higher light output color should make as
much light as a 75 watt incandescent (1170 to 1210 lumens), BUT:

1. A few fluorescent lamp colors are dimmer, such as Deluxe versions of
   cool white and warm white, and a few others.

2. Fluorescent lamps only make full light output in a somewhat narrow
   temperature range.  The fluorescents will probably not make full light
   when they first get started.  They typically make more light after warming
   up for a few minutes, then may lose a bit of light output if they warm up
   past optimum temperature.

3. Some ballasts do not make fluorescent lamps produce full light.  Some
   20 watt fixtures use a multi-purpose ballast designed to be usable 
with a
   few different wattages of lamps, and which typically sends about 16 watts
   of power to a 20 watt tube.  A few other ballasts send an inferior current
   waveform to the tube, impairing efficiency.  I have found some 
fixtures by
   "Lights of America" to suffer slightly impaired efficiency from a less
   smooth current waveform generated by an instant-start ballast system that
   starts "preheat" tubes instantly without a starter.  Some cheaper rapid
   start and trigger start ballasts produce slightly inferior current

   Some of the slightly popular 2-tube 20 watt "trigger start" ballasts
   are cheap and "fussy", and only work well if everything is optimum.
   These ballasts often don't work well with cool temperatures, slightly
   low line voltages, or slightly weak lamps.  Their best may not be too
   great anyway.  The same may be true of some cheaper two-tube 40 watt
   "shop light" ballasts.

4. Some fluorescent lamp colors (especially warm white, white, and cool
   white) have a spectral distribution that dims most reds and most greens.
   This may make things look dimmer.  For details of this effect, look for
   the appropriate section in
   (A web document of mine related mostly to discharge lamp mechanics)

"What will happen if I replace the two T20s with higher powered lamps? (If
 some will burn out, can I replace it as well?"

The ballasts in nearly all 20 watt fixtures will not send much over 20
watts of power to any size tube.  Sometimes even not much over 16 watts 
to any size tube.  You need a different fixture, more fixtures/tubes, or
possibly tubes of the same wattage but better brightness and/or color
brightening (more modern '3000', 'D830', '3500', 'D835', '4100', or 'D841'
tubes with higher lumen ratings but of wattage and size for the fixture).

Replacing fluorescent lamp or fixture components:

Most of these parts are easily replaced and readily available.  However,
it is usually necessary to match the original and replacement fairly
closely.  Ballasts in particular are designed for a particular wattage,
type and size, and tube configuration.  Take the old ballast with you
when shopping for a replacement.  There may be different types of sockets
as well depending on the type of ballast you have.
It is also a possible fire hazard to replace fluorescent tubes with a
different wattage even if they fit physically.  A specific warning has
been issued about replacing 40 W tubes with 34 W energy saving tubes, for
example. The problem is that the ballast must also be correctly sized for
the new tubes and simply replacing the tubes results in excessive current
flow and overheating of the ballast(s). 

Why are those tiny tiny 4 watt fluorescent bulbs so expensive?:

Can you say 'supply and demand' and 'economies of mass production'.  You
are comparing the price of the common F40CW-T12 lamp manufactured by the
zillions and sold in home centers for about $1 with specialty bulbs used
in a relatively few devices like battery powered fluorescent lanterns and
makeup mirrors.  These little bulbs may indeed cost up to ten times as
much as the much larger ones. 

By any measure of materials and manufacturing cost, the 4 foot bulb is much
much more expensive to produce.  There is nothing special involved.

How much energy is required to start a fluorescent lamp?:

(From: John Gilliver (

The amount of energy used in starting isn't worth worrying about. 
However, in addition to the turn on/off deterioration, there is also the
steady-state `on' deterioration (they don't last for ever even if left
on), so ... 

As far as turn-on deterioration:

I can't give it as a percentage, but for ordinary striplights I heard a
figure of 15 minutes (about 15 years ago), i. e. turning it on stresses it
as much as leaving it on for that long. Things have perhaps changed by now
(and there are so many kinds these days as well). 

For low-energy use, I'd go for fluorescents any day, unless size is a
major factor (Bosch [I think] and others have been trying to get some sort
of discharge lamp for headlights for some time, but I haven't seen any
yet). You might also look into LEDs, but I doubt they will match the
efficiency; certainly only the high-effificiency types (all seem to
consume about 10, 20, or 30 mA, but the output power in light seems to
vary widely, from a few millicandelas to about three candelas!). They are
narrow band (i. e.  coloured) as well of course. 

How do fluorescents lamps fail?

(From: Charles R. Sullivan (charless-at-crissy.EECS.Berkeley.EDU)).

The usual failure mode is depletion of the emission mix on the filaments.
Then they do not emit electrons, and the arc can't be sustained.  Unless
the ballast supplies a high enough voltage that very high field can be set
up near the electrode.  Then the ions bombarding the electrode have a high
The usual failure mode is depletion of the emission mix on the filaments.
Then they do not emit electrons, and the arc can't be sustained.  Unless
the ballast supplies a high enough voltage that very high field can be set
up near the electrode.  Then the ions bombarding the electrode have a high
enough energy to knock electrons out of the 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 see. enough energy to knock electrons out of the 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 see. 

-- end V1.72 --

Up to Lighting <- The Krib This page was last updated 29 October 1998