How CFL Bulbs Work

By: William Harris & Sascha Bos  | 
A spiraled CFL bulb lit up against a black background
The compact fluorescent light bulb stands poised to replace Edison's most famous invention as the icon of ideation. Fuse / Getty Images

As the symbol of innovation, the incandescent light bulb is not very innovative. It hasn't changed much since Thomas Edison introduced it in 1879. It still generates light by heating a tungsten filament until it reaches 4,172 degrees Fahrenheit (2,300 degrees Celsius) and glows white-hot.

Unfortunately, all of that white light is not very green. Only 10 percent of the electricity needed to power a bulb goes toward making light. The rest is wasted as heat. In the 2000s, the CFL bulb seemed poised to replace incandescent light bulbs — so, what happened?


What Are CFL bulbs?

Compact fluorescent lamps, or CFLs for short, contain argon and mercury vapor housed within a spiral-shaped tube. They also have an integrated ballast, which produces an electric current to pass through the vaporous mixture, exciting the gas molecules.

In older CFLs, it took several seconds for the ballast to produce enough electricity to ramp up the excitation. Newer CFLs have more efficient ballasts and require a shorter warm-up.


Either way, when the gas gets excited, it produces ultraviolet light. The ultraviolet light, in turn, stimulates a fluorescent coating painted on the inside of the tube. As this coating absorbs energy, it emits visible light.

Benefits of CFL Bulbs

When CFLs became commercially available in the 1990s, they offered numerous benefits compared to incandescent light bulbs.

Energy Efficient Lighting

CFLs use 75 percent less energy than incandescent light bulbs. That means CFLs require less wattage to produce an equivalent amount of light. For example, you could use a 20-watt CFL and enjoy the same amount of light as a 75-watt incandescent.


If every home in the U.S. made one such swap, Energy Star estimated that enough energy would be saved in one year to light more than 3 million homes.

Reduced Costs

Of course, if you're using less energy, your energy costs are going to go down. Replacing a standard 60-watt bulb with a 13-watt CFL can save a single household $30 in energy costs over the life of the bulb [source: General Electric].

Even with the higher price tag of CFLs, they still save you money compared to incandescent. That's because CFLs last a long time. In some tests, they burned brightly for 10,000 hours, whereas incandescent bulbs burned for just 800 to 1,500 hours [source: Johnson].

Environmental Impact

The environment comes out ahead, too. A good deal of electricity coming from fossil fuel–burning power plants gets directed to the lamps and light fixtures inside your house.

If you're saving energy by using CFLs, then you're pulling less electricity from the power grid. This reduces the amount of fossil fuel that must be burned, which reduces emissions of greenhouse gases. In a single year, the use of CFLs over incandescent bulbs removes as much greenhouse gas pollution as taking 800,000 cars off the road [source: Illinois EPA].


Drawbacks of CFL Bulbs

Compact fluorescent light bulbs do have a few issues that put people off. First, they deliver their best results when left on for 15 minutes or longer. Switching CFLs on and off will shorten their life and may decrease their efficiency, mainly because the excitation of the gases and of the fluorescent coating take some exposure to an electric current to reach an optimal level.

CFLs are also inefficient in enclosed, recessed fixtures (too hot) and in the fixtures of garage-door openers (too much vibration).


Finally, CFL bulbs can, in rare cases, interfere with electronic equipment. This interference is caused by infrared (IR) light, which CFLs produce and which IR readers can interpret as a signal.

CFL Bulbs and Mercury

If there is an ugly truth about CFL bulbs, it's the mercury they hold within their glass covers. Mercury is a persistent and highly toxic chemical. Most humans are exposed to the poison by eating fish contaminated with methyl mercury. However, it's also possible to inhale elemental mercury vapor, like the kind used in compact fluorescent light bulbs.

So why is it there? As we mentioned earlier, mercury vapor is required to convert electrical energy to radiant energy. When stimulated by electric current, mercury vapor inside a CFL produces ultraviolet light, which is re-radiated as visible light when it strikes the fluorescent compound, known as phosphor, painted on the inside of the bulb.


No other element has proved as efficient in this process, so even though the amounts of mercury used in bulbs has decreased over time, a small amount of mercury is still required for CFLs to function properly.

How Much Mercury Is in CFL Bulbs?

One CFL bulb typically requires approximately 0.000176 ounces (5 milligrams) of mercury. Older home thermometers contain 100 times that amount (0.0176 ounces or 500 milligrams), and many manual thermostats contain 600 times that amount (0.106 ounces or 3,000 milligrams) [source: GE Consumer & Industrial Lighting].

So, a single CFL bulb has very little mercury. And none of the chemical is released as long as the bulb remains intact.

How to Clean Up Broken CFL Bulbs

A broken CFL bulb can expose a person to mercury vapor. A tiny amount of solid mercury powder can also be released. For these reasons, extra caution should be taken when cleaning up a broken CFL. The U.S. Environmental Protection Agency (EPA) recommends following four easy steps:

  1. First, turn off your central heating or cooling system so fumes aren't moved from one room to another. Then open up the windows and let the room ventilate for 15 minutes.
  2. Next, it's time to clean up the broken bulb. Put on gloves to make sure you don't touch any of the mercury powder. Use a piece of cardboard to scoop up large pieces of glass. Switch to sticky tape to pick up small fragments and shards. Don't use your vacuum cleaner, and make sure all broken pieces, tape and cardboard are placed in a plastic bag.
  3. Finally, wipe the area with a damp paper towel and place the used towel in the plastic bag, as well.
  4. Seal the bag and immediately throw it away.


Recycling CFL Bulbs

IKEA and Home Depot both provide free disposal and recycling of used CFL bulbs.
© BlackJack3D

So what do you do with a burned-out CFL bulb if it contains mercury? First, you should realize that compact fluorescent bulbs are considered hazardous household items, a category that also includes paint, batteries and thermostats.

You must dispose of such items properly, which means you can't simply throw them away in household garbage.


To find out your options, start by calling your local waste management authority. You can also call 1-800-CLEANUP, a service provided by Earth911 that allows anyone with telephone access to search the organization's database of 100,000 recycling and hazardous waste collection locations for more than 170 different materials. You can search the same database online at

More and more retailers are stepping up to help with CFL bulb recycling. IKEA was the first retailer to provide free disposal and recycling of used CFLs. The Home Depot joined IKEA in 2008 by launching a national in-store consumer CFL bulb-recycling program in all of its nearly 2,000 locations. Some Ace and True Value stores are offering similar programs.


The End of CFLs?

For a time, CFLs presented a great alternative to incandescent bulbs. That is, until LED light bulbs came on the scene. LED bulbs are even more efficient than CFLs, and they don't contain mercury.

In 2022, the Biden-Harris administration proposed new legislation that would increase energy efficiency requirements for light bulbs from 45 lumens per watt to 120 lumens per watt, effectively banning CFLs, which produce up to 70 lumens per watt.


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