The Fluorescent Lamp

The greatest development in lighting since the 1879 incandescent
History (1938 first commercially available - Today)

Introduction & Statistics	Ballasts
How They Work	Design Variations
Inventors and Developments	Timeline

Fluorescents 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.

The standard 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.

Common uses:
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.

Advantages

-Energy 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 harsh shadows)

Disadvantages

-Flicker of the high frequency can be irritating to humans (eye strain, headaches, migraines) -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 overheat -There is a small amount of mercury in the tubes -Irritating flicker at the end of the life cycle

Statistics -CRI 74-90 -Color Temperature - comes in all variations, 5600 K for normal indoor applications -46 - 105 lumens per watt -Lamp life: 10,000 - 45,000 hours (does not take into account ballast life) Left: Early fluorescent tubes, available in various color temperatures

Below: general video on the fluorescent lamp. 8 min.

 

1. How the Fluorescent Lamp Works

We discuss two types of fluorescent lamps: Hot Cathode, Cold Cathode

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.

1A. Hot Cathode

1B. Cold Cathode

1A. How it works: Hot Cathode

The most common fluorescent lamp is the hot cathode:

Parts:
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.

How it works:
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).

Note: 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.

1.) 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.

2.) 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.

2a. 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 preheat fluorescents.

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 a plasma.

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 the process.

2b. 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.

3.) 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.

Powdered 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.

4.) 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.

Phosphors 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

1. Filament electrodes are preheated and glow red 2. The Cathode begins to ionize argon gas surrounding it 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

Ballasts

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.

Magnetic 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 limits current.

Why do we need a ballast? 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.

How it works: the Magnetic Ballast

The transformer 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.

Weaknesses: 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. Left: Historic ballasts galore at the Edison Tech Center's storage building

Above: electronic ballast in a CFL

Electronic 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+. Electronic ballasts 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 in China.

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.

1B. 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.

The Cold 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: the Geissler Tube, Plucker Tube, Cathode Ray Tube, thyratron, krytron, and dekatron.

Cold Cathode Lamps

Neon 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 1970s

Advantages

-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

Disadvantages

-They use a complex ballast
-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

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2. Design Variations Right: 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)

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3. Inventors and Developments:
The 80 year road to the modern fluorescent lamp.

Below: our YouTube video highlighting the inventors and their contributions:

	1856 - Heinrich Geissler 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
	1859 - Alexandre-Edmond Becquerel 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
	1891 - Nikola Tesla 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
	1896 - Thomas Edison 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
	1895 - Daniel McFarlan Moore achieved 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
	1901 - Peter Cooper Hewitt 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
	1911 - William D. Coolidge 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 later on. Schenectady, New York Photo: General Electric
	1915 - Georges Claude 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. Paris, France
	1926 - Edmund Germer 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 persuade investors. Berlin, Germany
	1927 - Albert W. Hull 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, New York Photo: Edison Tech Center
	1934 - George Inman 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. Nela Park (GE), Cleveland, Ohio Photo: The Schenectady Museum
	1934 - Richard Thayer worked with George Inman on the first modern fluorescent lamp. See the timeline below for more details. Nela Park (GE), Cleveland, Ohio Photo: The Schenectady Museum
	1934 - 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. Schenectady, New York / Nela Park, Cleveland, Ohio
	1976 - Edward E. Hammer 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: Ed Hammer
	1984 - John M. Anderson 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 technology. Read more on Anderson's work. Schenectady, New York Photo: John Anderson. home.frognet.net/~ejcov/anderson.html

Myths 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?"

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Development Timeline:

Early History: the invention was developed one part at time over many years.

1856 - 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, Germany

1890s - 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.

1895 - 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

1901 - 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

1911 - 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

1915 - 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

1934 - 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.

1934 - 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 1938 - 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 starter. 1976 - 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 institute. Left: Ed Hammer and his first successful prototype - now located at the Smithsonian Institute in Washington D.C.

1970s - 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 buildings.

1980s - 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:

READ MORE DETAIL: Fluorescent Lamp Development - a comprehensive history by Rick DeLair (historic lighting collector)

An original 1939 daylight fluorescent tube at the Edison Tech Center, visit us.

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Lamps are presented in the order of chronological development

Previous: Sodium Lamps 1920

Next: Halogen Lamps 1953

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Article by M. Whelan with assistance from Rick DeLair
Photos, video stills and video by M. Whelan

Sources:
John D. Harnden Jr.
Rick Delair - lighting collector
The General Electric Story by the Hall of History
Workshop of Engineers. John Miller. 1953
Wikipedia
US Patent Office
Smithsonian Institute

Photos:
Edison Tech Center
Schenectady Museum
Smithsonian Institute

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