Compact fluorescent light (CFL) bulb FAQ
Find out how and why compact fluorescent light (CFL) bulbs can be a smart money-saving
alternative to regular incandescent and halogen bulbs.
Can an electronic timer or photocell be used with a CFL?
It will depend on the bulb and the electronic timer or photocell you use. Start by checking the
bulb to verify that it can be used with electronic timers or photocells. This information is often
listed on the packaging. Next, check with the electronic timer or photocell manufacturer to find
out if the device you have is compatible with compact fluorescent bulbs. Using CFLs in
incompatible products will result in a shorter light bulb life.
Can an enclosed light fixture be used with a CFL?
Indoors, generally speaking, yes—provided the enclosed fixture is not recessed. Totally
enclosed recessed fixtures (for example, a ceiling fan light with a cover over the bulb) create
temperatures that are too high to allow the safe use of a CFL.
Many CFLs can be used outdoors in an enclosed fixture. Check the light bulb or packaging to
make sure it is approved for outdoor use, and verify the lowest operating temperature for the
area where the product is being used. If the bulb or package does not state it can be used
outdoors, then it is not approved for outdoor use, even in an enclosed fixture.
Can a dimmer switch be used with a CFL?
To use a compact fluorescent bulb on a dimmer switch, you must buy a bulb that's specifically
made to work with dimmers (check the package). Using a regular compact fluorescent bulb
with a dimming switch is not recommended. This use can shorten bulb life. (Using a regular
compact fluorescent bulb with a dimmer will also nullify the bulb's warranty.)
If the light bulb will be turned on/off frequently, should I use a CFL?
It’s not recommended. Frequently switching CFLs on and off will shorten their lives, make them
less efficient and save you less money in the long run. Compact fluorescent light bulbs can take
up to three minutes to warm-up and reach maximum efficiency.
They work best if they are left on for over 15 minutes each time they are turned on.
Can vibrations from a ceiling fan or garage door opener affect CFLs?
Vibration can cause the electronics in the CFL to fail. Therefore, using bulbs for these purposes
is not recommended.
How should a broken CFL be handled?
Carefully clean it up while wearing chemical-resistant gloves like those that are sold in
supermarkets and used for household cleaning. The gloves protect skin from getting cut by the
glass as well as from absorbing mercury, a hazardous substance used in all fluorescent light
bulbs. It’s okay to put a single CFL in the trash because it contains only a small amount of
mercury. But when disposing of a large quantity of CFLs, follow state and federal regulations for
mercury-containing light bulbs.
Why does the color of a CFL seem different when first turned on?
It’s the result of phosphor activation. Phosphor is the coating on the inside of the bulb that
gives the bulb a "white" light effect. Different phosphor combinations produce different colors
(like pink or purple) when first turned on and may have slightly varying response times.
Are hazardous amounts of ultraviolet (UV) light given off by CFLs?
No. The amount of UV produced by most light bulbs, including fluorescent, is far less than the
amount produced by natural daylight.
How does a compact fluorescent light bulb work?
Fluorescent bulbs don't use heat to create light, which makes them far more energy-efficient
than regular incandescent bulbs. Regular bulbs create light by heating a filament inside the
bulb; the heat makes the filament white-hot, producing the light that you see. A lot of the
energy used to create the heat that lights an incandescent bulb is wasted. A fluorescent bulb,
on the other hand, contains a gas that produces invisible ultraviolet light (UV) when the gas is
activated by electricity. The UV light hits the white phosphor coating inside the fluorescent
bulb, and the coating changes it into light you can see.
What CFL will replace a 60-, 75-, 100- or 150-watt regular bulb?
While a regular (incandescent) light bulb uses heat to produce light, a fluorescent bulb creates
light using an entirely different method that is 4–6 times more efficient. This means that you
can buy a 15-watt CFL that produces the same amount of light as a 60-watt regular
incandescent bulb. Plus fluorescent light bulbs last up to 13 times longer and use 2/3 to 3/4 less
electricity than incandescent bulbs with similar lumen ratings.
Comparison of the watts needed by regular incandescent bulbs vs. CFLs to produce the same
amount of light:
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20 watts incandescent = 5 watts CFL
28 watts incandescent = 7 watts CFL
36 watts incandescent = 9 watts CFL
40 watts incandescent = 10 watts CFL
52 watts incandescent = 13 watts CFL
60 watts incandescent = 15 watts CFL
75 watts incandescent = 20 watts CFL
100 watts incandescent = 26–29 watts CFL
150 watts incandescent = 38–42 watts CFL
250–300 watts incandescent = 55 watts CFL
How much heat (or infrared radiation) is emitted by regular, halogen and
compact fluorescent light bulbs?
Because incandescent and halogen bulbs create light through heat, about 90% of the energy
they emit is in the form of heat (also called infrared radiation). To reduce the heat emitted by
regular incandescent and halogen light bulbs, use a lower watt bulb (like 60 watts instead of
100).
Fluorescent light bulbs use an entirely different method to create light. Both compact
fluorescent bulbs and fluorescent tubes contain a gas that, when activated by electricity, hits a
coating inside the fluorescent bulb and emits light. This makes them far more energy efficient
than regular incandescent bulbs. The fluorescent bulbs used in your home emit only around
30% of their energy in heat, making them far cooler.
What is ENERGY STAR®, and why are many compact fluorescent light bulbs
ENERGY STAR labeled?
ENERGY STAR® is a voluntary partnership that includes the U.S. Department of Energy, the U.S.
Environmental Protection Agency, product manufacturers, local utilities and retailers. Partners
help promote energy-efficient products by labeling them with the ENERGY STAR logo and
educating consumers about the unique benefits of energy-efficient products. ENERGY STARlabeled products use less energy than other products, save money on utility bills and help
protect the environment.
Many CFLs are ENERGY STAR labeled because they are energy-efficient alternatives to standard
incandescent bulbs. A compact fluorescent uses approximately 75% less energy than a standard
incandescent bulb and can last many times longer. The super efficient performance of CFLs can
save at least $25 in energy costs over the life of each CFL that replaces an incandescent bulb.*
*Based on a minimum life of 6,000 hours at $0.10 kWh.
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