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How do Fluorescent Lights Work?

Fluorescent lights illuminate by passing an electric current through mercury vapor, which emits ultraviolet light. This UV light then excites a phosphor coating inside the tube, producing visible light. It's an energy-efficient process that has lit our spaces for decades. Curious about the science behind this everyday technology and its impact on our world? Let's delve deeper into the fascinating world of fluorescent lighting.
R. Kayne
R. Kayne

Fluorescent lights are far more complex in design than incandescent light bulbs, and more efficient. An incandescent light bulb generates very little light relative to the amount of heat it generates, wasting much energy. Fluorescent bulbs waste very little energy and generally last up to six times longer than incandescent bulbs. They are tubular in design, with capped ends that feature two external pins each. The inside of the glass tube is powder-coated with phosphorous, and a small drop of mercury is also placed inside the bulb, which is filled with argon gas. An electrode at either end connects to electrical circuits.

A basic understanding of how light is produced is helpful. Atoms have negatively charged electrons orbiting the nucleus at various distances. When an atom absorbs enough energy it can cause one of the electrons to jump to a higher orbit. As the electron loses energy, it falls back to its previous orbit. When it does so, it emits a photon of light. The key in producing light then, is in exciting atoms enough to knock electrons from their orbits.

Fluorescent light bulbs are more efficient than incandescent bulbs.
Fluorescent light bulbs are more efficient than incandescent bulbs.

When electricity flows through the electrodes in fluorescent lights, it produces a charge that causes free electrons to travel through the gas-filled tube from one electrode to the other. This energy vaporizes a small portion of the mercury inside the tube. Electrons and ions (charged atoms) collide with gaseous mercury atoms, which in turn release ultraviolet (UV) photons.

Fluorescent bulbs are more complex and more efficient.
Fluorescent bulbs are more complex and more efficient.

As humans cannot see UV light, there is one more step in the elaborate design of fluorescent bulbs. They key is in the phosphorous coating that lines the inner glass tube. When phosphor is exposed to UV light, it absorbs the energy and radiates it back out as visible light. This is where fluorescent lights excel over incandescent bulbs, as the UV energy wasted as lost heat in a traditional light bulb is transformed into visible light instead.

Fluorescent lights create light by using electricity to excite mercury vapor.
Fluorescent lights create light by using electricity to excite mercury vapor.

Since atoms are generally stable with a neutral charge and only become charged or ionized when they gain or lose an electron, fluorescent lights have varied starting mechanisms to get the ball rolling inside the tube. Older lights used a starter switch mechanism that sometimes took a minute or so to fully ionize the gas. In the interim, the light would flicker. Today’s bulbs have an ionizing trigger built into the ballast, which is the small device that controls the electrical current that feeds the electrodes.

Fluorescent lights use less energy and last up to six times longer than incandescent lights.
Fluorescent lights use less energy and last up to six times longer than incandescent lights.

The structure of an atom dictates the kind of photon produced, and therefore the wavelength or color of light. Although fluorescent bulbs are much more efficient than incandescent bulbs and last much longer, people generally prefer the light from old fashioned bulbs in the home, as it is closer to the red wavelength. This makes it appear “warmer.” The bright glow of fluorescent bulbs is shifted towards the “cooler,” blue spectrum. News bulbs designed for home use often use a phosphor blend that provides warmer light than older fluorescents.

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Discussion Comments


I was looking to replace the old Hubbell 120/270vac 20 amp tamper proof switches at the church. When I took the covers off I found each switch has three screws, with one wire to each. The top left is 110v. The bottom right is 20volts.

When switched "on," the bottom 20+ volts move to the left side? Each switch controls two dozen 8' tube lights that apparently the ballast were changed over to fluorescent? Anyone know of a replacement switch with a toggle?


My two fluorescent lights stopped working. I replaced both bulbs and one flickers and the other does not light up. Does the mean that the ballast is burned out, and I need a new light set?


with the power off from the switch and from the circuit breaker, will a fluorescent bulb light up for a couple of seconds when installed in the light fixture?


i have an eight-foot light that i got from a local convenience store (recycled). it began to only have one bulb lit. i purchased an additional bulb but it didn't light either. i purchased a new ballast and now neither bulb works. what did i do wrong?


I have two fluorescent light fixtures (two bulbs each) in an area of my basement near a shower. The bulbs have been burning out frequently, far sooner than they should. I suspect the humidity problem that anon36526 referred to. Do you think that's my problem?


In post 9 by Ellie Fagen, yes, there is definitely an inherent eerie quality to fluorescent lighting and it goes beyond the

the visible output spectrum, most lighting naturally operates at line frequency, 60 Hz.

An incandescent filament will tend to average the the light output at line frequency however a fluorescent is flashing on and off 60 times a second, to illustrate, watch a fan blade “strobe” under fluorescent lighting, this quality is most un-nerving to machine operators.

In industry and health care institutions many solutions have been applied, from 3 phase fixtures, (1 phase will be at max voltage every 120 degrees) to rotary converters which would operate fluorescents at 300Hz and above.

The advent of “electronic ballasts” when imaginative designers are committed to quality lighting, they will give us freedom from most of fluorescent lightings weirdness, but a true color corrected phosphor, naw, I'm dreaming.


you have to check the electrical line that any interruption of power occurs during the rain fall


Fluorescent tubes do light up under high voltage lines, but not to the brightness they have when connected to an electrical source. You could not read under this light. The tube also has a noticeable flicker. I have done this under a 345 KV line


Ambient electrical charge in the air from High Tension Wires. Air has a positive charge, Earth is negative, might cause a current such as electrostatic current,causing the fluorescent bulb to glow. Caution! do not come anywhere near high voltage lines. You do not have to touch the lines to be electrocuted!


foranon19075 go to the post by anon36526. His solution i perfect but I would also clean the tubes contacts, ideally with pure acetone(not fingernail polish remover) as it leaves no residue(do this in a well ventilated area.) it would be good to also clean the fixture's contact(electricity off!) and coat them with WD40 using a saturated Q tip. 36526 is correct about the factory coatin being cheap but tubes by GE, Sylvania and Phillips are dirt cheap and the makers casnnot afford anything of quality. I retired from the only manufcturer of Hi grade fluorescents in the world and we did not have the problems detailed by all the posters but the price was high though justified by the quality of the light produced and longevity. remember that no one can make a Rolex for the price of a Timex.


I enjoy fluorescent lights and the new energy-saving bulbs, but my background is sci-tech and art/health, and there is something wrong for us in these light sources.

The mildly-eerie light from fluorescent lighting casts unhealthy-looking color tones on things and on people, who seem to be purple and green in spots from it.

And the phosphorescence itself is so minutely spooky that we miss it, and yet...there is "something - just something" that is not quite right.

Flourescents have been around for more than 50 years and I'll bet they will, if they can, get rid of this disturbing aspect of fluorescent lighting. Comment welcome. elle fagan


How does an electronic ballast work with fluorescent tube light? It lights up even at low voltage and instantly.It is claimed to consume much less power. I have installed in my home four fitting with this type of ballasts.


annon19075....the humidity had condensed on the tube and has caused a "short" across the outside of the tube shunting enough power to prevent to tube from lighting. easy fix: wash tube with ammonia and re-coat with silicon. use a silicon spray from you local hardware store, not WD-40. A product labeled pure silicon would be the best choice. it would be wise to do all your tubes as the factory silicon coating is a low cost coating. repeat every 2-3 years to get max life from tube.


my TCL2127U doesn't turn on. the standby lamp is not lit when it is switched on. The power cord is tightly plugged to the outlet. what causes this problem?


Is it true that if you hold a fluorescent tube in your hand when standing under high tension power lines, the fluorescent tube will light up even though it is not connected to any power source. How does this occur if it is true ?


Bad contact (dirty or loose somewhere) or damaged electrical cord. I would first uninstall the tubes and reinstall them, making sure the contacts are clean and tight on each end. If your fixtures are older you probably have ballasts visible in each light canopy. Make sure they are connected properly and that when you touch or move them the light doesn't flicker. Ballasts get hot, so do this when the lights have just been turned on and the ballasts are still cool. Next check the cord that runs from the canopies to the wall. A damaged cord can allow in moisture. Finally I'd check the wall outlet to make sure the cord plugs in nice and tight to the wall. If none of this helps, the light fixtures themselves should probably be replaced. Save the tubes. There's nothing wrong with those.


why do 2 of my shop fluorescent lights not work only when it's raining?

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    • Fluorescent light bulbs are more efficient than incandescent bulbs.
      By: Deyan Georgiev
      Fluorescent light bulbs are more efficient than incandescent bulbs.
    • Fluorescent bulbs are more complex and more efficient.
      By: nao5970
      Fluorescent bulbs are more complex and more efficient.
    • Fluorescent lights create light by using electricity to excite mercury vapor.
      By: bannerwega
      Fluorescent lights create light by using electricity to excite mercury vapor.
    • Fluorescent lights use less energy and last up to six times longer than incandescent lights.
      By: Christophe ROURE
      Fluorescent lights use less energy and last up to six times longer than incandescent lights.