are a large family of light sources. There are three main types of fluorescent
lamps: cold cathode, hot
cathode, and electroluminescent.
They all use phosphors excited by electrons to create light. On this
page we will discuss the cold and hot cathode lamps. Electroluminescent
lamps use "fluorescence" but are so different they are
covered on another page. From
this point when we refer to 'fluorescent lamp' we will be talking about
a lamp with a glass discharge tube and fluorescent coating on the inside,
this is how the cold and hot cathode type of lamps are designed. Induction
lamps are a form of fluorescent lamps but they don't have electrodes.
We have a separate page for them here.
fluorescent lamp was developed for commercial use during
the 1930's. The idea of the fluorescent lamp had been around since
the 1880's however it took steady work over the decades to finally create
a working commercially viable model. This work was done by many, not
one single inventor. See our inventors list
to learn more.
lamps both outdoor and indoor, backlight for LCD displays, decorative
lighting and signs, both high bay and small area general lighting. Not
used for lighting from afar due to diffused nature of the light.
efficient, so far the best light for interior lighting
-Low production cost (of tubes, not of the ballasts)
-Long life of tubes
-Good selection of desired color temperature (cool whites
to warm whites)
-Diffused Light (good for general, even lighting, reducing
of the high frequency can be irritating to humans (eye strain,
-Flicker of common fluorescent light looks poor on video,
and creates an ugly greenish or yellow hue on camera
-Diffused Light (not good when you need a focused beam such
as in a headlight or flashlight)
-Poorly/cheaply designed ballasts can create radio interference
that disturbs other electronics
-Poorly/cheaply designed ballasts can create fires when they
-There is a small amount of mercury in the tubes
-Irritating flicker at the end of the life cycle
-Color Temperature - comes in all variations, 5600 K for normal
-46 - 105 lumens per watt
-Lamp life: 10,000 - 45,000 hours (does not take into account
Early fluorescent tubes, available in various color temperatures
Below: general video on the
fluorescent lamp. 8 min.
Simple Explanation Hot
and Cold Cathode Lamps:
Fluorescent lamps work by ionizing mercury vapor in a glass tube. This
causes electrons in the gas to emit photons at UV frequencies. The UV
light is converted into standard visible light using a phosphor coating
on the inside of the tube.
most common fluorescent lamp is the hot cathode:
This lamp consists of a glass tube filled with an inert gas (usually
argon) at low pressure. On each side of the tube you will find a tungsten
electrode. The ballast regulates AC power to the electrodes.
Older lamps used a starter to get the lamp going. Modern lamps use pulse
start which is done by components within the ballast.
Step by step explanation of a standard 4 foot long 40 watt straight
tube lamps (this is the most popular size of fluorescent lamp in the
world since the 1940s).
There are two kinds of ballasts, the magnetic ballast which uses copper
coils (transformers), and the electronic ballast. Electronic ballasts
are favored today because they use a lot less material and are lower
cost to produce.
AC electric current passes through the ballast. The ballast will step
up 120 AC volts (in the US) to 216 V, next the power passed through
a 'choke' or 'reactor', this limits current and prevents the lamp from
creating a type of short circuit which would destroy the lamp. All arc
discharge lamps need a choke to limit current.
The lamp's glass tube is called a discharge tube and it works by having
electrons pass from one electrode to the other. This forms what is called
an "arc". Getting this started is a real challenge.
To get the lamp started you
need a spike of high voltage to get the arc started. The colder
the lamp is, the higher voltage you need to get a start. The voltage
'forces' current through the argon gas. Gas has a resistance, the colder
the gas, the higher the resistance, therefore you need a higher voltage
with colder temperatures. Since creating a high voltage is a challenge
and dangerous, engineers figured out ways to 'preheat' the lamp, that
way less of a high voltage is required. There are different ways to
start a lamp including: preheat, instant start, rapid start, quick
start, semi-resonant start and programmed start. We will tell you
about the main two ways to make it start.
Use a Starter (startswitch) - This method is the first
and arguably the most reliable type of way to start a lamp according
to some. Many facilities still have older fixtures with startingswitch
Watch an animated schematic
on our YouTube video below:
1.) In the early systems
the starter contained a small neon or argon lamp. When the starter
was cool at first, current ran through the starterswitch through
the neon lamp. The 1 W lamp would warm a bimetallic strip in the
starter, while in the main arc tube the current passed through the
tungsten electrodes which would make them heat up and ionize some
of the gas. This 'preheated' the lamp.
2.) Current passes through
the tungsten electrodes on each end of the lamp. The electrodes
are like a filament on an incandescent lamp, when current passes
through they heat up and give off free electrons. This process of
letting off free electrons is called thermionic
emission. The free electrons ionize the argon gas in
the tube. The first gas to be ionized is right around the filament,
you can see it clearly in the photo above. An ionized gas is called
3.) When the starter
switch (with the little neon or argon lamp inside) gets warm enough,
the bimetallic strip flips the other way, completes the circuit,
bypassing the small lamp. The lamp goes out and the entire circuit
shorts. During the short the voltage falls to zero. The bimetallic
strip cools and pops back open, opening the circuit. In the ballast
the transformer had a magnetic field, when the circuit is cut the
magnetic field collapses and forms an 'inductive kick' from the
ballast. Suddenly this kick of high voltage is sent through the
lamp and this starts the arc. If it didn't work, if the lamp is
still too cold, then the starter switch will light again and repeat
Rapid Start - This modern
type of starting method constantly preheats the electrode (cathode)
using low voltage AC power. The arc is started by passing through
a grounded reflector or starting strip on the outside of the glass
tube. The arc starts between the electrode and the starting strip
first and rapidly propagates through the entire discharge tube. The
schematic for this and other modern start methods is much more complex.
So now your arc has started and current passes from your
cathode to your anode (electrode to electrode) through the argon gas.
Because your dealing with AC power, the cathode switches back and forth.
AC power is good for the lamp because if the lamp was DC, the cathode
side would be brighter and more intense since there are more free electrons
spewing off of the tungsten electrode there. Also if the lamp was on
DC power, the electrode which is acting as the cathode would become
weaker as it lost tungsten atoms and the lamp would not last as long.
Since we use AC the electrons or ions break off one side, reach the
other, then on the next cycle are sent back. Also the lamp tube has
a nice uniform brightness on both ends.
phosphors on the inside of the tube absorb the UV light. Here you can
see the UV light as a purplish light. The quartz lamp used in this experiment
is the same as a compact fluorescent lamp except that it has no phosphor.
Vaporizing mercury and making light: The
normal fluorescent lamp has a small amount of mercury in the tube. On
a cold tube you would see it as a couple of pinhead sized dots if you
were to break the tube so you can see inside. The arc which started
in argon gas quickly warms up the mercury liquid stuck to the side of
the tube. The mercury boils or vaporizes into the arc stream. The arc
easily passes through vaporized mercury. This creates UV light. That
light is emitted and strikes the phosphors on the inside of the glass
tube. The phosphors convert the light into useful visible light.
are chemically designed to give off a certain color. Here you see a
warm white at 3000 Kelvin (color temperature) and cool white which is
closer to daylight at 6000 Kelvin
Filament electrodes are preheated and glow red
2. The Cathode begins to ionize argon gas surrounding
3. This lamp is powered by AC power, so the cathode switches
to the other side and you see the left side begin to ionize,
the other side (now the anode) stays warm and ionized
4. The left side cathode warms to full and both sides
are warmed up
5. The ballast provides a high voltage kick which instantly
ionizes the entire tube to a high level of brightness
6. The lamp returns to normal voltage and its warmth has
vaporized all the mercury, the lamp operates as normal
on the Science:
does electricity flow through the gas? In a solid metal
wire electrons jump freely from atom to atom, while the atoms
stand stationary. In a gas there are also free electrons "jumping"
their way from the negative electrode to the positive at the other
side. What is different is that you also have ions moving as well.
is an ion? An ion is an atom with positive or negative
charge. If an atom has one extra, or one less electron than normal,
it will have a + or - charge. In an ionized gas the negative ions
will flow/move towards the positive electrode.
do you get gas ionized? Normally you could not send
current through a gas, but if you introduce free electrons and
ions into the glass tube you can ionize the gas. This is done
by have a filament electrode, current heats up the filament which
boils off electrons into the tube, this ionizes the gas
Watch the video above
to learn the basics about different types of ballasts.
Ballasts are a fascinating part of the fluorescent lamp system due to
the complex nature of resistance, inductance and reactance. There are
two kinds of ballasts: the magnetic ballast, and the electronic ballast.
Ballasts: magnetic ballasts use transformers to convert and
control electricity. Understanding the ballast takes some background
because it uses the complex property of induction
The ballast raises voltage, but the most important thing is that is
Why do we need
As current forms
an arc through the lamp, it ionizes a higher percent of gas
molecules. The more molecules are ionized, the lower the resistance
of the gas. We know that no resistance will equal a short. So
without the ballast to control the current, current would rise
so high that the lamp would melt and destroy itself.
it works: the Magnetic Ballast
which is called a "choke" in a ballast is a coil of wire called
an inductor. It creates a magnetic field.
The more current you put through, the bigger the magnetic field, however
the larger magnetic field opposes change in current flow. This slows
the current growth. Since we are dealing with AC power, the current
flows in one direction for only 1/60th or 1/50th of a second, then drops
to zero before flowing in the opposite direction. Therefore the transformer
only has to slow current flow for a moment.
The magnetic ballast operates at lower frequencies than an electronic
ballast, it also rarely can fail and drip hot tar. Tar is used
to insulate the transformers in the ballast and reduce the humming
noise. Some older fixtures have a capacitor with PCBs inside,
but it is a very small amount, about one teaspoon. Equally electronic
ballasts have phenol, arsenic and their own set of contaminants.
Historic ballasts galore at the Edison Tech Center's storage
electronic ballast in a CFL
Ballasts: The electronic ballasts use semiconductors to limit
power to a fluorescent lamp. First the ballast rectifies the AC power,
then it chops it to make a high frequency for improved efficiency. The
ballast can more precisely control power than a magnetic ballast but
does have a number of problems.
The design is quite
different for each lamp. Some lamps only need a simple resistor
to control power. LEDs need a low power resistor for current
control. The resistor is not acceptable for larger power lamps
because it creates a lot of waste heat and therefore reduces
efficiency. Electronic ballasts usually change the frequency
of power to a lamp from 50/60 Hz to 20kHz+.
are usually viewed as being more efficient because by running
a lamp at a higher frequency you get more efficacy or brightness
from the lamp above 10kHz. This is in theory, however poorly
or cheaply constructed ballasts will ruin the advantage of the
electronic ballast. Most electronic ballasts are cheaply constructed
Manufacturers use as little
copper and other expensive materials as possible. Components have less
ability to deal with heat and rigors of long life. Regular fluorescent
lamps (discharge tube assemblies) have the ability to be highly efficient,
but poorly made ballasts are the limiting factor. Electronic ballasts
also have a way of failing prematurely due to overheating and this limits
the great life of the lamp. The stated life of a lamp on the box usually
is not to be believed.
How it works: Cold Cathode Fluorescent Lamps
The Cold Cathode Lamp is
different from a Hot Cathode in that it has
an interior coating that more easily creates free electrons when used
with higher voltages.
Cathode device was not born as a light source. It is an evacuated tube
filled with gas with an electrode at each end. The earliest cold cathode
tubes included the Geissler tube (1857) which was used for science and
entertainment (provided an amusing glow depending on the gas within).
Over the years cold cathode tubes were developed to perform a variety
of functions including counting, voltage regulation, radio detection,
phase angle control in AC, computer memory, radio frequency transmission,
high voltage control switches, and more. Early devices were called:
Tube, Plucker Tube, Cathode Ray Tube, thyratron, krytron, and dekatron.
Cold Cathode Lamps
Lamps and Cold Cathode Fluorescent Lamps (CCFLs) create light as
their primary function. Neon Lamp is a term describing lamps with a
tube smaller than 15 mm in diameter.
Applications of CCFLs:
-Back lighting for LCD screens
-Computer monitors (tube)
-Television Screens (LCD, CRT)
-Alcove lighting and background diffused indirect lighting
-Nixie Tubes - early form
of numeric display, they are small glass tubes shaped as numbers, activated
by a wire mesh anode and multiple cathodes, replaced by LEDs in the
-CCFLs come on instantly at full brightness
-They are more reliable starting in cold weather
-They have a long life
-They are dimmable to some degree
-Light created is easier on the human eye
-They use a complex
-Not a full range in dimmability
-New devices in LCD screens are not as energy efficient as Cathode Ray
Tubes of the past when used as a Television/Monitor
A giant compact fluorescent along with a U-shaped configuration,
"twisty" bulb CFLs, Circline, and other shapes. All
of these variations are on display at the Edison Tech Center
in Schenectady, New York. Contact us for public hours. See the
video below: History of Consumer Fluorescent Lamps where
Rick DeLair shows us the various designs along with years and
companies. (Hot Cathode Lamps)
Inventors and Developments:
The 80 year road to the modern fluorescent lamp.
Below: our YouTube video
highlighting the inventors and their contributions:
1856 - Heinrich
was the first to extensively study the arc tube. His Geissler
tube was the foundations for all arc discharge lamps including
HID lamps Bonn, Germany
first used phosphors on the inside of a glass discharge tube.
He was the first to use a phosphor coating but it was 30 years
later before others really put the phosphor coating idea back
into the spotlight. 70 years later the first phosphor coatings
were developed with a acceptable color and commercialized. Paris, France
created an induction lamp. This lamp had greenish unpleasant
phosphors. It was not really a "fluorescent lamp"
as we know today because it did not have electrodes. His high
frequency ballast was a predecessor to modern high frequency
ballasts used in modern fluorescent ballasts. We have another
webpage just on induction lamps
here. New York City, New York
made a light that used a calcium tungstate phosphor coating.
The phosphors were excited by x-rays in a glass tube. The lamp
had very short life and unpleasant color. Clarence Dally helped
Edison build the lamp, but died after exposure to radiation.
Edison developed a healthy fear of x-rays after his death and
abandon the project. West Orange, New Jersey
success developing the first predecessor to the fluorescent
light called the Moore Tube. The tube looked very much like
today's light except that it was longer and used CO2 and Nitrogen
to make a pink and white light. His lights were reliable and
sold to department stores in the New York City area. The lamp
was short lived in that it was expensive to replace and the
Mercury Vapor lamp was competition. East Orange, New Jersey Photo:
The Schenectady Museum
developed the first commercial mercury vapor lamp. An electric
arc through mercury vapor is the basis for the modern fluorescent
lamp. It would be another 20 years before mercury vapor was
experimented with in the fluorescent lamp. Hewitt's work with
electrodes and ballasts formed a basis from which fluorescent
lamps operate. New
York, New York
developed ductile tungsten wire which revolutionized the incandescent
light bulb. The material also happened to be perfect for all
arc discharge lamps and vacuum tubes and x-ray tubes. Tungsten
has one of the highest melting points of any metal which made
it a robust material for making electrodes in fluorescent lamps
Schenectady, New York
invented the modern neon lamp. This lamp is actually a simple
type of fluorescent lamp. It uses neon and argon gas and has
two electrodes in a tube. Original neon lamps did not use a
phosphor. It is considered a cold cathode fluorescent lamp.
came very close to developing the modern fluorescent lamp. His
lamp used UV rays from mercury vapor. It glowed a greenish color
due to his phosphors, but had a short life. The hostile conditions
in the arc tube corroded the electrodes and destroyed the lamp.
If more attention had been paid to his work and more funds invested,
he might have finished developing the lamp.
The ugly green color did not help him
had contributed much in the field of vacuum tubes, he was able
to build of the work of Moore whose patents were bought by General
Electric. Hull was able to develop a stronger UV emission from
the tube. Most importantly he developed a way to make electrodes
that would not disintegrate. He set the stage for the final
advancements 6 years later. Schenectady,
Edison Tech Center
along with Richard Thayer, Eugene Lemmers, and Willard A.
Roberts develop the first true fluorescent lamp. Their lamp
has real white phosphors, is stable, reliable, and their design
has not changed much in 78 years.
- Clifton G. Found and Willard
Roberts w C.A.
Nickel and G.R. Fonda
(Schenectady) all work on better phosphors for more light output
with better white colors. They discover the use of zinc-beryllium
silicate and magnesium tungstate.
New York / Nela Park, Cleveland, Ohio
develops the CFL or compact fluorescent lamp at Nela Park. He
did not patent the lamp early on and GE though it would be too
expensive to manufacture. Later on the spiral tube design spread
and became the lamp we know today. Hammer works under original
light creator Richard Thayer. In addition to this Ed Hammer
also developed more efficient straight tube lamps starting with
the F-40 Watt Miser. Nela
Park, Cleveland, Ohio Photo:
developed many improvements in the fluorescent lamp: short arc
fluorescent lamp, fluorescent lamp without ballast, improved
electrodes and fluorescent lamp dimming technology. Anderson
was a professor at Rensselaer Polytechnic Institute and employee
of General Electric with 27 patents 1970 - 1992 related to lamp
more on Anderson's work. Schenectady,
John Anderson. home.frognet.net/~ejcov/anderson.html
about the fluorescent lamp and inventors:
The internet has permitted
growth of myths about many technologies due to web authors using unsupported
facts from dubious websites. As you can see from the list above Nikola
Tesla and Agapito Flores did not invent the fluorescent lamp. Many poorly
researched internet sources will claim they did. Most of these sources
are "content farms" which pump out online articles with less
than one hours work on the part of the author. This means no proper
research was done. Wikipedia can be edited by anyone and therefore is
also prone to inaccuracies created by fanatics of Tesla and Flores.
Read more about the Flores and Tesla issue here:
"Who Invented the Fluorescent Lamp?"
the invention was developed one part at time over many years.
- The evacuated arc tube:
Heinrich Geissler was able to evacuate a glass tube, put two electrodes
on the ends and make a lamp with a faint glow do to trace amounts of
gas left over inside the tube (an accident). This work was the basis
for Sodium, Mercury Vapor, Xenon arc, MH, and Fluorescent lamps. Bonn,
Use of fluorescent coating, high frequencies:
Thomas Edison and Nikola Tesla separately pursued the idea
of fluorescent lamps. Edison lamps used a calcium tungstate as a fluorescent
coating. Tesla used a high frequency model that made a greenish light.
All of these attempts failed to be commercially successful due to short
lamp life, poor reliability, and poor light color.
- Use of fluorescent coating, high frequencies:
Daniel McFarlan Moore developed the first commercial predecessor
to the fluorescent lamp called a Moore Tube. The tubes were 2-3 meters
long and were installed in offices and shops. Unlike the modern fluorescent
lamp his device used an electric arc in CO2 or Nitrogen to make a white
an pink light. It was much more efficient than the incandescent lamp.
The problem was that the system was very expensive to install and used
very high voltages (a danger to humans working on them). East Orange, New Jersey
- Use of mercury vapor arc to create UV light (critical to lighting
up the modern fluorescent) and use of a ballast with the lamp:
Peter Cooper Hewitt developed the first commercial mercury
vapor lamp. While some had experimented with using mercury vapor
in Germany and England, Hewitt's design was able to produce a bright
high quality light with a wide enough spectrum of emitted light to be
usable. This lamp produced UV rays which would turn out to be useful
later on. A ballast was located above the lamp to create a reliable,
controlled power source. New York, New York
- Invention of ductile tungsten used in the electrodes:
William D. Coolidge develops ductile tungsten for use in incandescent
bulbs at General Electric in Schenectady. This miracle material finds
use in many other lamps such as halogen, sodium, mercury vapor, fluorescent,
and more. It is a wire which is wrapped into a filament or electrode.
Schenectady, New York
- Development and commercial success of Neon lamps.
Georges Claude developed this cold cathode lamp which lead the way
to the fluorescent lamp. Paris, France
1926 - First
fluorescent lamp to use UV:
Edmund Germer built a low voltage fluorescent lamp similar to the
modern fluorescent. It used UV rays to excite phosphors. The color of
the lamp was an unpleasant greenish color and the product was never
fully developed. His lamp is considered the first fluorescent lamp,
however a lot of work still needed to be done to make the lamp have
a decent lifespan. Berlin, Germany
1927 - Electrode
design in the fluorescent lamp:
Albert W. Hull develops a tungsten electrode which would not disintegrate
and created a stronger UV light. Some of this work had been based on
the work of Leroy J. Buttolph at GE in 1919. Albert Hull was also the
developer of many electron tubes, improved xray, and numerous other
developments.General Electric bought Germer's patents in order
to continue work on the lamp. Schenectady, NY
- The first modern fluorescent lamp! 1.) Arthur H. Compton (inventor of the sodium
vapor lamp at Westinghouse, 1920) visits Oxford, England. He meets
with local lamp inventors who are working with a 2 ft long tube with
yellow-green colored phosphors. He writes to William L. Enfield at General
Electric. 2.) William Enfield leads a group to develop a fluorescent
lamp which would be a white color, and have reliability sufficient for
commercial sale. Nela Park, Ohio.
3.) By November George Inman, Richard Thayer, Eugene Lemmers, and
Willard A. Roberts develop the first modern fluorescent lamp.
It is 10 inches long 3/4 diameter and used zinc silicate phosphor (phosphor
is the work of Willard A. Roberts). Nela Park, Ohio.
- Clifton G. Found and Willard Roberts (Nela Park)
work with C.A. Nickel and G.R. Fonda (Schenectady)
develop better phosphors zinc-beryllium silicate (white) and
magnesium tungstate (daylight white). Nela Park, Schenectady
- The first fluorescent lamps were released under the
GE product line as Mazda "F" lamps in sizes 18",
30" and 36" long and 1" in diameter. By 1939
Westinghouse was selling the lamps as well with an improved
- Edward E. Hammer develops the compact fluorescent
lamp while working under Richard Thayer at Nela Park (Cleveland,
OH). Hammer's CFL worked at curbing reflective losses by spacing
his spiral design in a certain way. The lamp is not patented
early and GE thought that the 28 million dollar cost to build
a production facility was too much. The prototype sat in Hammer's
office and it is theorized that visitors from competing companies
copied the design. The first prototype was donated to the Smithsonian
Ed Hammer and his first successful prototype - now located at
the Smithsonian Institute in Washington D.C.
In the 1970's
it was found that a diameter of 38 mm gave the greatest efficiency.
The 40 W 1200 mm x 38 mm lamp became the most used lamp in commercial/industrial
- John Anderson advances the fluorescent lamp by improving
the electrodes, inventing a dimmable fluorescent lamp
The Bright Stik: The Bright Stik
is a type of fluorescent that was developed by John H. Harnden at General
Electric. It uses a F20 T12 tube and the ballast as a resistance, it
does not use a transformer.
For a comprehensive
early history on the invention and development of the fluorescent lamp
see the link below:
by M. Whelan with assistance from Rick DeLair
Photos, video stills and video by M. Whelan
John D. Harnden Jr.
Rick Delair - lighting collector
The General Electric Story by the Hall of History
Workshop of Engineers. John Miller. 1953
US Patent Office
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