Sam's F-Lamp FAQ
Fluorescent Lighting,electronic ballast, and Light Fixtures
Principles of Operation, Circuits, Troubleshooting, Repair
Version 1.90
Copyright (C) 1994,1995,1996,1997,1999
Samuel M. Goldwasser
--- All Rights Reserved ---
Corrections or suggestions to: sam@stdavids.marconimed.com
Reproduction of this document in whole or in part is permitted
if both of the following conditions are satisfied:
- This notice is included in its entirety at the beginning.
- There is no charge except to cover the costs of copying.
1-800-683-8825
Principles of Operation, Circuits, Troubleshooting, Repair
Table of Contents
Back to Table of Contents.
Preface
Author: Samuel M. Goldwasser
Corrections/suggestions: sam@stdavids.marconimed.com
Copyright (c) 1994,1995,1996,1997,1998,1999
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.
We will not be responsible for damage to equipment, your ego, county wide
power outages, spontaneously generated mini (or larger) black holes, planetary
disruptions, or personal injury or worse that may result from the use of this
material.
Thanks to Don Klipstein
(don@misty.com) for his comments and
additions to this document. His Web site
(http://www.misty.com/~don/) is a
valuable resource for information relating to lighting technology in general
and also includes additional articles dealing with fluorescent and other
discharge lamps.
Back to Table of Contents.
Introduction
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
initiate 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: Some specialty UV lamps emit shortwave or medium wave UV which
is harmful and should not be used without appropriate protection or in an
enclosure which prevents the escape of harmful UV radiation.)
Fluorescent lamps are about 2 to 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.
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.
Back to Table of Contents.
Safely Working with Fluorescent Lamps and Fixtures
There aren't many dangers associated with typical fluorescent lamps and
fixtures:
- 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.
- Fluorescent lamps and fixtures using iron ballasts are basically pretty
inert when unplugged. Even if there are small capacitors inside the
ballast(s) or for RFI prevention, these are not likely to bite. However,
you do have to remember to unplug them before touching anything!
- However, those using electronic ballasts can have some nasty charged
capacitors so avoid going inside the ballast module and it won't hurt to
check between its outputs with a voltmeter before touching anything.
Troubleshooting the electronic ballast module is similar to that of a
switchmode power supply. See the document: Notes on the
Troubleshooting and Repair of Small Switchmode Power Supplies
- Nasty chemicals: While the phosphors on the inside of fluorescent tubes
are not particularly poisonous, there is a small amount of metallic mercury
and contact with this substance should be avoided. If a tube breaks, clean up
the mess and dispose of it properly and promptly. Of course, don't go out
of your way to get cut on the broken glass!
And take care around sharp sheet metal!
Back to Table of Contents.
Fluorescent Fixtures and Ballasts
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
available.
- 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.
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
value.
Ballasts must generally be fairly closely matched to the lamp in terms
tube wattage, length, and diameter.
Instant start, trigger start, rapid start, etc. ballasts include loosely
coupled high voltage windings and other stuff and do away with the starter:
- 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.
- The ballast for a rapid start fixture has in addition small windings for
heating the filaments reducing the required starting voltage to 250 to
400 V. There are probably the most common types in use today. Trigger
start fixtures are similar to rapid start fixtures.
- The ballast for an instant start fixture has a loosely coupled high
voltage transformer winding providing about 500 to 600 V for starting
in addition to the series inductor. The electrodes of "instant start"
bulbs are designed for starting without preheating. In fact, they are
shorted out internally and are thus incompatible with preheat and rapid
start ballasts (and they have only a single pin at each end!). The
electrodes still emit electrons due to thermal emission but since they are
shorted out cannot be pre-heated. That is why they require a higher
starting voltage from the ballast. They they light instantly, but this
slightly reduces lamp life.
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).
(From: Vic Roberts (kirther@ix.netcom.com).)
The most basic ballast is nothing more than a current limiting device, such
as an inductor, resistor or capacitor. For 50 and 60 Hz applications, the
most common current limiting device is an inductor.
A simple current limiter works best when the line voltage is at least 2 times
the lamp voltage. So, a simple inductor can be used in Europe, where the line
voltage is 220 to 240 VAC, to operate a 4 foot lamp, which operates at 85 to
100 volts, depending upon design.
In the US and other places that use 120 VAC lines the ballast is a
combination autotransformer (to raise the voltage) and inductor (the
current limiter).
In addition, a Rapid Start ballast has additional windings to supply about
3.6 VAC to heat the filaments.
(From: Asimov (Asimov@juxta.mn.pubnix.ten).)
A ballast is a simple transformer with a very high impedance secondary
winding which makes its current self-limiting. It also has windings for
each lamp filaments. At startup the filaments get most of the power and
heat up to facilitate ionization.
Meanwhile the secondary builds up a very high EMF which finally fully
ionizes the plasma between both filaments. At this point the effective
resistance of the conducting plasma is quite low and the current flow is
limited by the secondary's impedance. This also partially saturates the
core and as consequence reduces power to the filaments.
The usual failure in ballasts is that the secondary's insulation
deteriorates and it starts leaking to ground. Often because the proper
wiring polarity was not observed. The secondary can thus no longer
generate the high EMF required to start the plasma conducting.
The KISS test method is to use a known good lamp. If it lights, the
ballast is good too. The ballast can also be tested with the power off by
checking for continuity in the filament windings and a very high
resistance to ground for each filament. Don't try this with power on!
(From: Craig J. Larson (larson@freenet.msp.mn.us).)
Call Magnetek, a ballast manufacturer on 1-800-BALLAST. Ask for a copy
of their Troubleshooting & Maintenance Guide for Linear Fluorescent
Lighting Systems. Its a nice little guide book for teaching you the basics.
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. However, this is not always the case
and depending on design (mainly how much filtering there is on the rectified
line voltage), varying amounts of 100/120 can still be present.
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
controls.
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:
Back to Table of Contents.
Fluorescent Fixture Wiring Diagrams
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 |
+-------------+
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 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.
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:
- OFF: Both switches are open.
- ON: Power switch is closed.
- 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.
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.
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) -|-------+
'-------------------------'
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----/ ----------|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 -|-------------+
'----------------------'
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 (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-----------------------------+
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.
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-----------------------------+
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
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---+-------------------+ +-----+
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!
For reasonable distances, this should work reliably and be safe provided that:
- 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.
- 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.
- 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).
(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 Table of Contents.
Specialty Fluorescent Lamp Types
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.
(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", 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
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.
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:
- They are often physically larger than the incandescent bulbs they replace
and simply may not fit the lamp or fixture conveniently or at all.
- The funny elongated or circular shape may result in a less optimal
lighting pattern.
- 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.
- Some types (usually iron ballasts) may produce an annoying 120 Hz
(or 100 Hz) flicker.
- Ordinary dimmers cannot be used with compact fluorescents.
- 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.
- There may be an audible buzz from the ballast.
- They may produce Radio Frequency Interference (RFI).
- 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!
- Due to the high up-front cost, the pay-back period may approach infinity.
- 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.
(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!
Back to Table of Contents.
Troubleshooting of 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.
- Bad fluorescent tubes. Unlike incandescent lamps where a visual
examination 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.
- 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. If
both ends glow a dim orange color, then the filaments' emissive coating
may or may not be in good shape. It takes approx. 10 volts to form an
arc across a healthy fluorescent lamp filament.
- 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 will
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.
- 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.
- 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.
(From: Don Klipstein (don@Misty.com).)
Fluorescent tubes failing in this manner normally draw reduced current. The
voltage across the tube is higher and the tube will sometimes draw more power,
but the current flowing through the ballast is less.
Since the ends of the bulb usually burn out unequally, some "net DC" may try
to flow through the ballast. My experience is that the feared core saturation
effects do not occur. Furthermore, the common rapid start ballasts have a
capacitor in series with the secondary windings which would block any DC.
There is a different problem that I once knew of causing a fire: Starters
getting stuck in the "closed" state. The symptom is the ends of the tube
glowing brightly, either yellow-orange or a color closer to the normal tube
color, sometimes even one end glowing yellow-orange and one end glowing a more
normal color. Excessive ballast current flows in this case. This is not a
problem with "instant start", "rapid start", or "trigger start" fixtures. It
is only a problem where there are starters.
A dim orange or red-orange glow more likely indicates dead tubes on a rapid
start or trigger start ballast. If the fixture is a preheat type, dim orange
end glow indicates less current than a brighter yellow-orange, and the ballast
is less likely to overheat. Different brands of ballasts are designed a
little differently.
If a preheat fixture has the tube glowing only in the ends, it is recommended
to immediately remove the tube to stop the ballast from possibly overheating.
You should replace both the tube and the starter. The starter is bad if this
occurs, and the tube is usually bad also. Typically, the starter goes bad
after too much time trying to start a bad tube. In the unlikely event the
starter had the initial failure, the tube will be damaged by prolonged
excessive end glow.
Many fluorescent fixtures will not start reliably unless they are connected
to a solid earth (safety) ground. This is most likely the case with rapid or
trigger start magnetic ballasts. These will usually state on the label:
"Mount tube within 1/2 inch of grounded metal reflector". If this is not done
or if the entire fixture is not grounded, starting will be erratic - possibly
taking a long or random amount of time to start or waiting until you brush
your hand along the tube.
The reason is straightforward:
The metal reflector or your hand provides a capacitive path to ground through
the wall of the fluorescent tube. This helps to ionize the gases inside the
tube and initiate conduction in the tube. However, once current is flowing
from end-to-end, the impedance in the ballast circuit is much much lower than
this capacitive path. Thus, the added capacitance is irrelevant once the tube
has started.
The reason that this is required is probably partly one of cost: it is cheaper
to manufacture a ballast with slightly lower starting voltage but require the
fixture to be grounded - as it should be for safety anyhow.
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 tightly
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 sheet
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. Also
see the section: Why do Fluorescent Lamps Buzz and What to Do
About It?.
(From Brian Beck (jrdnut@utah-inter.net).)
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.
"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:
- A few fluorescent lamp colors are dimmer, such as Deluxe versions of
cool white and warm white, and a few others.
- 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.
- 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
waveforms.
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. Also, some "shop light" fixtures that you may
think are dual 40 watt are actually dual 25 watt 4-foot fixtures.
- 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
http://www.misty.com/~don/dschtech.html
(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).
Complaints are generally of the following form:
"I just replaced my bulbs because they had the black bands at the end and
finally went out altogether. The new bulbs light fine but they have subtle
rings of light running down the inside of them."
or
"My fluorescent tubes look like a they have a writhing snake inside trying
to get out."
(From: Don Klipstein (don@Misty.com).)
The rings sometimes happens. I forget the name of this, but it is a sometimes
normal feature of the main discharge column in low pressure lamps. In
fluorescent tubes, it is more common if the bulb is cold or not fully warmed
up, brand new or not-yet broken in, or if the ballast is of poor quality or
there is a bulb/ballast mismatch.
Double check the label on the ballast and the lamp type to be sure they
are compatible with each other.
If the bulb is an "energy saver" 34 or 35 watt model (part number usually
begins with F40, which is the same for a normal 40 watt bulb), be sure the
ballast is compatible with that bulb. If it is compatible with both 34's and
40's, it is compatible with 35's. Matching bulbs/ballasts is important for
these models mainly to ensure long bulb life and to avoid overheating the
ballast. 34 and 35 watt bulbs are prone to rings and flickering and being dim
and being unusually sensitive to cold because of the nature of these bulbs and
can do so no matter what ballast you use. They will normally behave properly
after warming up, especially in ceiling fixtures where heat builds up.
Fluorescent tubes sometimes also "swirl" before being broken in, or if they
are underpowered by an incorrect or low quality ballast.
(From: Ken Berg (goken@inreach.com).)
The problem with premature lamp failures using Instant Start ballast lies in
the fundamental difference in the basic operating principles between Rapid
Start and Instant Start lamps. It has really nothing to do with whether the
ballast is magnetic or electronic. Instant Start ballasts are really designed
to be used with the standard T12 single pin Slimline lamps. Instant Start
ballasts deliver a higher striking voltage on starting than Rapid Start
ballasts do. Slimline (the single pin) lamps have a slightly heavier
cathode to tolerate the starting cycle. With Instant Start, the lamps are
really started "cold cathode" style, and then they of course run as hot
cathode.
On occasion, even the standard T12 Slimlines refuse to "die like gentlemen"
and flash and swirl wildly. Maintenance guys have known for decades that
they need to replace Slimlines promptly if they start doing this. They will
need to keep this in mind when dealing with the F32T8 lamps as well. Even
though the lamps are bi-pin, and so look like the old Rapid Start T12's,
they are more than likely running on an Instant Start circuit, and will
sometimes go like this.
The cathodes in most bi-pin lamps are made for Rapid Start, which is a
starting method that is easier on the filaments. The lamp manufacturers are
supposed to have already taken the starting characteristics of the new F32T8
Instant Start ballasts into account, but some might just be going on the
cheap, and skimping of the lamp filaments.
"I have been experimenting with 15 W T8 lamps running from a dimmable
electronic ballast. I have found that if set to a low light level after a
few days of being left on, one of the cathodes in the tube often goes open
circuit."
(From: Clive Mitchell (clive@emanator.demon.co.uk).)
The only explanation that I can come up with is that there isn't enough
current flow to keep the cathodes warm and this is causing the discharge
to be concentrated on a small point. The 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.
The voltage drop across this point will be higher than normal since the
heat being generated is being dissipated by the rest of the cathode and
this means that more power than normal is being dissipated from that
point causing sputtering. This could be causing the early burn-out.
The best way to validate this would be with a clear tube to see the
cathode discharge activity.
I've seen a phenomenon like this when I've lit a halide lamp at low
level with a small voltage multiplier circuit. The glow discharge led
to a white hot point on the electrode that caused sputtering.
If this is the case, then the cure is to use a ballast that can supply a
continuous heating current to the cathodes.
Back to Table of Contents.
Items of Interest
The original 4-foot fluorescent lamp was the F40T12, which is 47.75 inches
(approx. 121.3 cm) long from pin tip to pin tip and 1.5 inches (approx. 4 cm)
in diameter and designed to consume 40 watts. Not too many years ago, this
was the most common and least expensive fluorescent lamp.
There is the "HO" (high output) 4-foot tube and the "SHO" (super high output)
4-foot tube. These are not common and are only used where there is not
enough room to fit enough standard F40 tubes to make enough light. These
lamps are slightly less efficient than standard fluorescent lamps. These
tubes require more current than standard 4-foot tubes and require special
ballasts. These tubes should only be used with their respective ballasts, and
these ballasts should only be used with the tubes they were designed for.
In response to the energy shortages of the 1970's, the 34 watt lamp with
the same physical dimensions was introduced. It works in most 40 watt
fixtures and draws 34 watts in these fixtures. However, some 40 watt
ballasts can overheat with this lamp. The ballast should say that it is
rated for use with 34 watt lamps.
Please note that a 34 watt tube can say F40 and still be a 34 watt tube
and not be a 40 watt tube. It will in some way say near the F40 designation
that it is an energy-saving tube. There have also been a few 35 watt
tubes, which are similar enough to 34 watt tubes to work anywhere both 34
and 40 watt tubes can work. 34 watt lamps sometimes produce noticeably
less light than 40 watt lamps, especially in cooler environments.
Nowadays, there is the 25 watt "shop light" lamp. The 25 watt tubes should
only be used with appropriate 25 watt shop light ballasts, and these
ballasts should only be used with these tubes. Please do not confuse these
with other wattage tubes/fixtures of the same physical dimensions which are
also sometimes called "shop lights".
A more recent development is the 32 watt T8 lamp, which is 4 feet long but
only one inch (2.5 cm) in diameter. These require ballasts made for them.
Many of the ballasts made for these lamps are electronic ballasts.
The confusion has increased in recent years now that the USA has an
energy-conservation law against manufacturing and importing standard 40
watt white fluorescent lamps. Specialty lamps and white ones with a color
rendering index of at least 82 (out of a maximum of 100) are exempt and
are still available in the USA as true 40 watt lamps.
Again, be sure that you are not mismatching the bulb and the ballast.
If the ballast is not rated to operate the bulb type being used, the bulb
life will probably be shortened and the ballast life may be shortened. In
a few cases, the ballast may catch fire after failing.
At one time, most fluorescent lamps were "cool white" which is a plain-old
white with a color like that of of average sunlight.
One bad thing about "cool white" is that the spectrum of "cool white" has
a surplus of yellow and a shortage of green and red. Since mixing red
light with green light makes yellow, the white light of a cool white lamp
still looks white. Since yellow objects usually reflect green through red,
they look yellow as usual in this light.
But red objects reflect mainly red light and green objects reflect mainly
green light, and look dim and dull due to the shortage of red and green
wavelengths in "cool white". Impure reds and greens will look less red and
less green as well as darker - making them look more brown.
Other early whites were "warm white" and "daylight". Warm white is a color
similar to that of incandescent lamps, although it usually looks 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 unflattering ways.
Both "warm white" and "cool white" are obtained using "halophosphate"
phosphors. The surplus of yellow and shortage of red and green is a general
characteristic of halophosphate phosphors.
"Daylight" is a bluish white, and does not have as bad a surplus of yellow
as the other halophosphate whites. But it is also slightly dimmer.
Next were the "deluxe" versions of cool white and warm white. These have
"improved" halophosphate phosphors and are sometimes known as "broad spectrum"
lamps. They have a less severe yellow surplus and red/green shortage than
standard halophosphate lamps. They also produce slightly less light.
Another slightly common halophosphate white is "white", which is between
"cool white" and "warm white" in color.
Other halophosphate whites, whether of differing spectral quality or
different shade of "warmth/coolness" include "supermarket white", "sign
white", "north light", "merchandising white", etc. Please note that some
of these are not made by all fluorescent lamp manufacturers, and some of
the less standard color names are trademarks of their respective
manufacturers.
One earlier fluorescent lamp color with enhanced red spectral content is
the "natural". This lamp has "cool white" halophosphate phosphor with a
red-glowing phosphor of a different type added in. These 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 the usual halophosphate types which make skin tones
look green-yellowish. Some meat displays have "natural" fluorescent lamps
to make the meat look more red.
Nowadays, there are "triphosphor" fluorescent lamps. These have a spectrum
very different from that of the halophosphate lamps. Triphosphor lamps
have their spectral content mostly in distint bands and lines:
Orangish red, slightly yellowish green, green-blue, and violet-blue. For
cooler color lamps, there is an additional band in the mid-blue.
Triphosphor lamps do not distort colors as badly as halophosphate lamps,
and triphosphor's color distortions are usually not as unpleasant as those
of halophosphate. Also, triphosphor lamps often make reds and greens look
slightly brighter than normal, unlike halophosphate lamps which usually
make these colors look dimmer than normal.
Most compact fluorescent lamps and most 4-foot T8 (1-inch diameter) lamps
are triphosphor lamps.
Triphosphor lamps come in various warm and cool shades, usually designated
by "color temperature". This is the 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 common for compact fluorescent lamps, similar
to many incandescent lamps.
3000 or 30 - "warm white", similar to whiter shades of 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 the color of average sunlight.
5000 or 50 - an icy cold pure white like that of noontime tropical sunlight.
6500 or 65 - slightly bluish white or "daylight".
There are still other specialty whites, including ones with a mixture of
"broad spectrum" and "triphosphor" phosphor formulations to get a spectrum
more like that of daylight. Some others have particularly good "broad
spectrum" phosphors, sometimes mixed with other phosphors for a tailored
spectrum. Many of these, like most triphosphor lamps, have color
temperature designations.
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.
(From: John Gilliver (g6jpg@gmrc.gecm.com).)
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.
(From: Charles R. Sullivan (charless@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
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.
This is a common phenomenon with most common fluorescent tubes as they
age. However, frequent or repeated starting can accelerate the process. The
black areas in themselves don't affect operation except to slightly reduce the
amount of light available since the phosphor in that area is dead. However,
they do represent a loss of metal from the electrodes (filaments).
The cause is sputtering from the 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.
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).
(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.
"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.
(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 80% chance 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.
(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!
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.
Back to Table of Contents.
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