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!
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 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.
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 value.
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:
- 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.
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.
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:
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
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.
Wiring
for Rapid Start and Trigger Start Fixtures
Rapid start and trigger start fixtures do not have a separate starter or
starting switch but use auxiliary windings on the ballast for this function.
The rapid start is now most common though you may find some labeled trigger
start as well.
Trigger start ballasts seem to be used for 1 or 2 small (12-20 W) tubes. Basic
operation is very similar to that of rapid start ballasts and the wiring is
identical. "Trigger start" seems to refer to "rapid starting" of tubes that were
designed for preheat starting.
The ballast includes separate windings for the filaments and a high voltage
starting winding that is on a branch magnetic circuit that is loosely coupled to
the main core and thus limits the current once the arc is struck.
A reflector grounded to the ballast (and power wiring) is often required for
starting. The capacitance of the reflector aids in initial ionization of the
gases. Lack of this connection may result in erratic starting or the need to
touch or run your hand along the tube to start.
A complete wiring diagram is usually provided on the ballast's case.
Power is often enabled via a socket operated safety interlock (x-x) to minimize
shock hazard. However, I have seen normal (straight) fixtures which lack this
type of socket even where ballast labeling requires it. Circline fixtures do not
need an interlock since the connectors are fully enclosed - it is not likely
that there could be accidental contact with a pin while changing bulbs.
Wiring
Diagram for Single Tube Rapid or Trigger Start Ballast
Below is the wiring diagram for a single lamp rapid or trigger start ballast.
The color coding is fairly standard. The same ballast could be used for an
F20-T12, F15-T12, F15-T8, or F14-T12 lamp. A similar ballast for a Circline
fixture could be used with an FC16-T10 or lamp FC12-T10 (no interlock).
Power Switch +---------------------------+
Line 1 (H) o----/ ----------|Black Rapid/Trigger |
+------|White Start Red|------+
| +---|Blue Ballast Red|---+ |
| | +-------------+-------------+ | |
| | | | |
| | Grounded | Reflector | |
| | ----------+---------- | |
| | .-------------------------. | |
| +----|- Fluorescent -|----+ |
+------x| ) Tube ( | |
Line 2 (N) o----------------x|- (bipin or circline) -|-------+
'-------------------------'
Wiring
Diagram for Two Tube Rapid Start Ballast
The following wiring diagram is for one pair (from a 4 tube fixture) of a
typical rapid start 48 inch fixture. These ballasts specify the bulb type to be
F40-T12 RS. There is no safety interlock on this fixture. (A similar scheme
could also be used on a dual tube Circline fixture though slightly different
ratings may be needed for each tube since they would be of different sizes.)
Power Switch +--------------------------+
Line 1 (H) o----/ ----------|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 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-----------------------------+
Schematic for Rapid Start Ballast with Isolated Secondary
As noted, rapid start fixtures do not have a separate starter or starting switch
but use auxiliary windings on the ballast for this function. Here is the
schematic for a typical 1-tube rapid start fixture including the internal wiring
of the ballast.
This ballast includes separate windings for the filaments and a high voltage
winding that is on a branch magnetic circuit that is loosely coupled and thus
limits the current once the arc is struck. It is not known if this design is
common. The isolated secondary and separate high voltage winding would make it
more expensive to manufacture.
A complete fixture wiring diagram like those shown in the section:
Wiring for Rapid Start and Trigger Start Fixtures
will probably be provided on the label.
+-------+
Power Switch ||======||( |
Line 1 (H) o---/ ----+ || ||( +----+---------o to both pins
)|| ||( ( filament winding on one end
)|| ||( +--------------o
)|| ||( HV winding Grounded reflector
)|| || +=----^^^^^^^-------------------------+
)|| ||( _|_
)|| ||( +--------------o -
)|| ||( ( filament winding to both pins
Line 2 (N) o---------+ || ||( +----+---------o on other end
||======||( |
+-------+
Loose magnetic coupling in the ballast core results
in leakage inductance for current limiting.
Schematic of Rapid Start Dual Lamp Ballast
This ballast is marked "Rapid Start Ballast for TWO F40WT12 Lamps. Mount tubes
within 1/2" of grounded metal reflector". This circuit was derived from the
measurements listed in the section:
Measurements of a Dual Tube Rapid Start Ballast.
The autotransformer boosts line voltage to the value needed for reliable
starting with the filaments heated. The series capacitor of approximately 4 uF
is used instead of leakage inductance to limit current to the tubes. Leakage
inductance from loose magnetic coupling is used to smooth the waveform of
current flowing through the tubes. The .03 uF capacitor provides a return path
during starting to the yellow filament winding but is not really used during
normal operation.
Numbers in () are approximate measured DC resistances.
Red 1 o--------------------------+
8.5 V (.5) )|| Tube 1 Filament 1
Red 2 o----------------------+---+ ||
_|_ ||
4 uF --- ||
| ||
+---+ ||
)||
)||
)|| HV winding
)||
)||
+---------+---+ ||
| _|_ ||
| .03 uF --- ||
| | ||
Yellow o----------------------+---+ ||
8.5 V | (.5) )|| Tubes 1 and 2 filament 2
Yellow o--------------------------+ ||
| ||
| ||
Blue 1 o------------+-------------+ ||
8.5 V (.5) )|| Tube 2 filament 1
Blue 2 o--+-----------------------+ ||
| ||
+--> Black (H) o--+-----------------------+ ||
| )|| Primary of
115 V (13) )|| autotransformer
| )||
+--> White (N) o------------o/o-----------+ ||
Interlock ||
|
Green (G) o-----------------------------+
Measurements of Dual Tube Rapid Start Ballasts
One is a Universal, the other is a Valmont.
(Measurements made with Radio Shack multimeter)
Resistance:
Measurement Universal Valmont
------------------------ ----------- -----------
White-Black 13 13
Between blues .5 .55
Between reds .5 .55
Between yellows .5 .6
Black to closer blue <.1 <.1
Blue-red open open
Blue-yellow open 5 M
Red-yellow open 20 M
Capacitance:
Blue-red ~4 uF ~3.5 uF
Blue-yellow ~.03 uF
Red-yellow ~.03 uF
Primary current, (not true RMS), various secondary load conditions:
Secondary open .32 A .35 A
60W 120V incandescent bulb .75 A .63 A
Short .48 A .53 A
Heater voltage: not measured approx. 8 V, unsteady
surprisingly independent
of secondary load
Open circuit output voltage voltage (from one red wire to one blue one, highest
reading of four combinations):
Red-Blue 270 V 275 V
Fluorescent Lamps in Series?
This is not possible where line voltage is 105 to 125 VAC because this is not
sufficient to sustain the discharge where two lamps are in series. Special dual
lamp ballasts are required.
However, where the line voltage is 220 VAC, it is possible:
(From: andrew@cucumber.demon.co.uk (Andrew Gabriel)
Here in UK (and probably all 220 to 250V areas), this is common:
=======
L o---+-----^^^^^^^-------+ +-----+
| Ballast | | |
| (Inductor) +|-|+ |
| | - | |
| | | +-+
| Tube 1 | | |S| Glow Starter
| | | +-+
| | - | |
| +|-|+ |
| | | |
_|_ Power Factor | +-----+
___ Correction |
| Capacitor | +-----+
| | | |
| +|-|+ |
| | - | |
| | | +-+
| Tube 2 | | |S| Glow Starter
| | | +-+
| | - | |
| +|-|+ |
| | | |
N o---+-------------------+ +-----+
Fluorescent Lamps in Parallel?
Like most gas discharge tubes, fluorescent lamps are negative resistance
devices. Therefore, it isn't possible to put more than one lamp in parallel and
get them both to light - additional components are needed. The following applies
mostly to magnetic ballasted fixtures. Where electronic ballasts are used, all
sorts of games can be played to implement wierd configurations!
Multiple lamp fixtures in countries with 110 VAC power usually have special
ballasts with separate windings for this purpose. Where 220 to 240 VAC is
available, it may be possible to put multiple lamps in series with individual
starters. See the section: Fluorescent Lamps in
Series?.
However, there is at least one application where putting two lamps is parallel
makes sense: light fixtures in hard-to-reach or safety-critical areas where
redundancy is desirable. With only minor modifications at most, a conventional
single lamp ballast can be connected to a pair of lamps in such a way that only
one will light at any given time. (Which one actually starts could be random
without additional circuitry, however.) If either lamp burns out or is removed,
the other will take over. The ballast must provide enough power to the filaments
for starting but once started, the lamp that is on will operate normally and
there should be no degradation in performance or expected lamp life (except to
the extent that the unlit lamp's filaments might be kept hot).
The following is just a suggestion - I have not confirmed if or with which model
ballasts these schemes will work!
For rapid start ballasts, this could be as simple as wiring all connections to
the lamps in parallel - if the ballast has enough current available to power
both sets of filaments for starting. For trigger start ballasts, the filament
power is not an issue so it should be even easier:
Power Switch +---------------------------+
Line 1 (H) o----/ ---------|Black Rapid/Trigger |
+-----|White Start Red|--------+
| +--|Blue Ballast Red|-----+ |
| | +--------------+------------+ | |
| | | | |
| | +---------------+ | |
| | Grounded | Reflector | | |
| | ----------+---------- | | |
| | .-------------------------. | | |
| +----|- Fluorescent -|--|--+ |
| | | ) Tube ( | | | |
+--|----|- (bipin or circline) -|--|--|--+
| | '-------------------------' | | |
| | +---------------+ | |
| | Grounded | Reflector | |
| | ----------+---------- | |
| | .-------------------------. | |
| +----|- Fluorescent -|-----+ |
| | ) Tube ( | |
Line 2 (N) o---------+-------|- (bipin or circline) -|--------+
'------------------------'
Note: The interlock normally present on most rapid/trigger start fixtures have
been removed to permit one lamp to operate if other is removed.
For preheat ballasts, wiring the filaments in parallel would probably result in
insufficient current to either lamp for it to start reliably. If the filaments
were wired in series, one lamp would probably start, but if the filament of one
lamp burned out or the lamp was removed, the fixture would cease to function
kind of defeating the purpose of these gyrations!
Wiring Fluorescent Lamps to Remote Ballasts
For reasonable distances, this should work reliably and be 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).
Wiring diagram of Low Power 220 VAC Fluorescent Lamp
(From: Manuel Kasper (mk@mediaklemm.com).)
The circuit in Low Power 220 VAC
Fluorescent Lamp
is from an AC line powered 'light stick'. So there's no fancy inverter circuit
inside, but a simple ballast without any nasty coils - just capacitors,
resistors, and diodes. A few modifications would probably be necessary to make
it operate from 110 VAC. It runs the tube brighter than a similar lamp power
from a 12 V inverter. (See the section: "Automotive Light Stick Inverter" in the
document:
Various Schematics and Diagrams. FWIW, the brand is "Brennenstuhl".
It was damn hard to open up because everything was made out of thick plastic
with no screws (no wonder; it cost $6) - but thanks to a huge saw I managed to
get at the guts without destroying the tube or the circuit.
Specialty
Fluorescent Lamp Types
All
Sorts of Less Conventional Lamps
In addition to the boring white ones (OK, well 'white' does come in various
colors!), other interesting types of lamps include all sorts of real colors
(red, green, blue, yellow), blacklight lamps, germicidal lamps in which there is
no phosphor coating at all and a quartz tube to transmit short-wave UV light
(e.g., EPROM erasers and PCB photoresist activation), sunlamps, plant lights and
special purpose specific wavelength lamps such as reprography and copier lamps.
The basic technology is extremely flexible!
(From: Bruce Potter (s602531@aix2.uottawa.ca).)
There are also High Output and Very High Output types of lamps that have a
discharge current of 0.8 A and 1.5 A instead of the standard 0.3 A. HO and VHO
lamps are used when high light output is desired but are being outmoded by HID
lamps like metal halide.
Blacklight Fluorescent Lamps
(From: Don Klipstein (don@misty.com).)
BL in the tube designation (e.g., F40T12BL) means "blacklight", which is a
fluorescent lamp with a phosphor that emits the longest largely invisible UV
wavelengths that are both efficiently and fairly cheaply possible. This phosphor
seems to emit a band of UV mainly from 350 to 370 nanometers, in the UV-A range.
BLB means "blacklight-blue", 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.
Compact Fluorescent Lamps
These are miniaturized fluorescent lamps that usually have premium phosphors
which often come packaged with an integral ballast (either iron or electronic).
They typically have a standard screw base that can be installed into nearly any
table lamp or lighting fixture that accepts an incandescent lamp.
Compact fluorescents are being heavily promoted as energy savings alternatives
to incandescent lamps. They also have a much longer life - 6,000 to 20,000 hours
compared to 750 to 1000 hours for a standard incandescent. While these basic
premises are not in dispute - all is not peaches and cream:
- 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.
Cold
Weather Fluorescent Lamps
(From: Bruce Potter (s602531@aix2.uottawa.ca).)
There are special lamps with heavy glass jackets and/or with krypton gas filling
for cold weather/freezer applications. They work best at below
room-temperatures. It really annoys me when I go to the grocery store or see
outside installations with dim, flickering tubes! What a waste of electricity!
Troubleshooting of
Fluorescent Lamps and Fixtures
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.
- 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. Occasionally, 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.
Comments on Black Bands and Other Fluorescent Failure Issues
(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.
Why is
a Grounded Fixture Needed for Reliable Starting?
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.
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 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.
Why
Fluorescent Lamps are Sometimes Dimmer than Expected?
"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).
Rings
or Swirls of Light in Fluorescent Lamps
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.
Comments on Instant Start/Rapid Start Compatibility
(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.
Premature Cathode Failure in Dimmed Fluorescent Lamps
"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.
Items of Interest
All
Those Different Wattage 4-Foot and F40 and "Shop Light" Lamps?
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.
What's with All Those Different Shades of White?
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.
Why
Small Fluorescent lamps Cost More than 4-Foot Ones
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.
Energy Consumption and Wear-And-Tear due to Starting
(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.
What
Happens when Fluorescent Lamps Wear Out?
(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.
Blackening at Ends of Fluorescent Tubes
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.
Hot
Cathode Versus Cold Cathode Operation
The cathode is the negative electrode of a vacuum tube or gas filled discharge
tube. Current flows by way of electrons emitted from the cathode and attracted
to the positive electrode, the anode.
A hot cathode is one which must be heated to operate properly - to emit
sufficient electrons to be useful. Examples: TV and monitor CRTs, most vacuum
tubes (or valves), vacuum fluorescent displays (like those on your VCR). This is
called thermionic emission - the boiling off of electrons from the surface of
the cathode. Normal fluorescent lamps are hot cathode devices - partially
maintained by the discharge current itself. They all have some sort of warmup
period (though it can be quite short).
(From: Phil Rimmer (primmer@tunewell.com).)
A cold cathode is one where operation takes place without depending on heating
of the surface above ambient. There are all sorts of devices that use 'cold'
cathodes - neon lamps and signs, fluorescent backlight tubes, and helium neon
laser tubes. Naturally, cold cathode devices don't have much of a warmup
requirement.
The purpose of a cathode is to feed electrons into the negative end of the
positive column (the discharge) so they can variously excite and ionise gas or
vapour atoms.
Electrons are released from cathodes by the action of the positive ions being
accelerated towards them due to an electric field in the vicinity of the
cathode.
Electrons are broadly released in two ways: Thermal emission and secondary
emission.
- Thermal emission is the primary process used in "hot cathode" lamps which
include standard fluorescent tubes. The ions are accelerated towards the cathode
through a small cathode voltage (less than 10 volts) and gain just enough energy
to heat a small part of the very fine wire electrode when they collide with it.
They heat it until it glows dully and electrons are "boiled off", liberated by
the thermal energy. This process is very efficient in producing lots of
electrons and results in efficient lamps.
- Secondary emission is a more brutal process for generating electrons. It
requires an accelerating voltage drop of 130 to 150 volts. It is used in
cold-cathode lamps that have relatively huge cylinders of iron for electrodes.
These massive electrodes require much too much energy input to make them into
thermal emitters. The energetic ions simply "knock" electrons off the metal
surface. In so doing they also knock some of the metal off as well, a process
called sputtering. The big electrodes have enough material to last before other
effects cause lamp failure.
Hot cathode lamps operate in cold cathode mode if the cathode receives too
little energy to keep it glowing. The colliding ions are thirty times more
energetic than usual and soon sputter enough metal off the tiny electrodes to
destroy them.
Moral: Pre-heat the electrodes before starting the discharge and maintain
auxiliary current in the electrodes if the discharge current is low (e.g, when
dimming).
Comments on Small Inverter Powered Fluorescent Lamps
(From: Paul Bealing (paul@pmb.co.nz).)
Many small low cost inverters use a 2 transistor (one quite small) self
oscillating circuit. Simply minimum function, low cost. These circuits can be
quite efficient at low power levels. I have seen them used up to 50 watts.
Losses are usually in the transformer and the switching transistors. As the
currents increase, the losses usually increase for a given power output.
The lamp requires a high voltage, usually 300 to 500 V, to strike. The voltage
depends on the length/wattage of the lamp. Once struck, the current through the
lamp is limited to achieve the wattage. The voltage across a small running lamp
will be in the order of 60 to 100 volts AC.
Many simple inverters use a series resonant circuit to generate the high strike
voltage, which is disabled by the run current.
A couple of years ago I designed an inverter for a PL11 11 Watt lamp based on a
switchmode power supply controller IC, 2 power mosfets, and a push-pull
transformer, running at about 200 kHz. The main application was in diesel
locomotives running from 75 V DC. I've had the circuit operating down to 10V DC
(different transformer winding). The primary current rises and the dissipation
increases.
Operating a Fluorescent Lamp on DC
"I have a application in mind that will use a DC power source around 100 volts
and fluorescent lighting. What kinds of voltage do I need to sent the
fluorescent? Are there any good sources of info. for the circuitry I would
need?"
(From: Don Klipstein (don@Misty.com).)
If it is a preheat tube of 22 watts or less, the cheap-and-dirty way to do it is
to use a normal preheat fixture. The only change is to add a resistor in series
with the ballast. This resistor should be maybe 100 ohms for 20 and 22 watt
lamps, slightly higher for lower wattage ones. It should be able to safely
dissipate a wattage comparable to that of the lamp.
The above includes most simple "PL"/twin-tube compact fluorescent lamps with
removable bulbs with two pins, as well as most compact fluorescent bulbs with
"choke" type ballasts running from 120 volts AC.
Should you need anything more energy-efficient than this, then there is the
world of electronic ballasts.
BTW, most low-power-factor screw-in 120 VAC compact fluorescent lamps with
electronic ballasts work fine "as-is" with about 160 volts DC or squarewave.
Ballasts and PCBs (The Hazmat Type)
(From: David Morris (allane@ix.netcom.com).)
Ballasts that were made after the late 70's do not contain PCB's. I spoke with
an Advance and GE ballast rep. a few years ago about this and I was told the
only sure-fire method to tell that there are no PCB's is if the ballast says no
PCB's. Any ballast that doesn't say that has a better than 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.
Driving Cold Cathode Fluorescent Lamps
(From: David VanHorn (dvanhorn@cedar.net).)
Linear
Technology has several extremely detailed app notes written by Jim Williams
on this topic. It's more complicated than you might imagine to do it right. Just
making the tube light is perhaps only 10% of the job. The rest includes keeping
it running a long time without blackening, providing the ability to set the
brightness, not loosing all your energy to wiring capacitance, and not creating
an EMI nightmare.
Definitely read and understand those app notes, even if you go to another
vendor! The good news is that the actual circuit isn't that bad!
What
is the E-Lamp?
The E-Lamp is one of those inventions that sounds like a really good idea but
still hasn't (as far as I know) made it into wide scale production. In essence,
it is an RF excited compact fluorescent lamp. Some of the E-lamp's basic
characteristics include.
- Fits into standard household light bulb bases.
- Radio frequency radiation was emitted, then converted to light.
- Dimmable using standard phase control dimmer - no special devices needed.
- Very efficient so runs cool and consumes much less power than incandescent
lamps (don't know how it compares to compact fluorescents).
- Desirable white spectral characteristics.
- No filament to wear out (and no wires through glass) so potentially very
long life.
Aside from cost issues, there could also be concerns with respect to RF
emissions effects on health and interference with other household appliances and
electronics.
(Victor Roberts (robertsv@ix.netcom.com).)
E-lamps are electrodeless fluorescent lamps. They use a high frequency or RF
magnetic field to create a time varying electric field which in turn drives a
discharge which is very similar to the discharge in an ordinary fluorescent
lamp. Except for the means by which the discharge is created, these E-lamps and
identical to all other fluorescent lamps. There is no magic other than the fact
that electrodeless excitation allows for the elimination of the electrodes, so
electrode failure and wear out are no longer a problem. Also, electrodeless
excitation removes the requirement that the lamp be long and thin to achieve
high efficacy. Proof of this is beyond the scope of this note. :) Hence, an
electrodeless fluorescent lamp can be more easily made in the shape of an
incandescent lamp.
There are also electrodeless metal halide lamps and, of course, the
electrodeless sulfur lamp.
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