Energy.gov

Fluorescent Lighting

Fluorescent lightbulbs use 25%-35% of the energy used by incandescent bulbs to provide the same amount of light (efficacy of 30-110 lumens per watt). They also last about 10 times longer (7,000-24,000 hours).

The light produced by a fluorescent tube is caused by an electric current conducted through mercury and inert gases. Fluorescent lights require a ballast to regulate operating current and provide a high start-up voltage. Electronic ballasts outperform standard and improved electromagnetic ballasts by operating at a very high frequency that eliminates flicker and noise. Electronic ballasts also are more energy-efficient. Special ballasts are required for dimming.

The two general types of fluorescent lightbulbs are:

• Compact fluorescent lamps (CFLs) -- a type of screw-in bulb which is used in common household fixtures
• Fluorescent tube and circline bulbs -- typically used for task lighting such as garages and undercabinet fixtures, and for lighting large areas in commercial buildings.

See technical information and illustrations of fluorescent lighting on Energy Basics.

CFLs

CFLs combine the energy efficiency of fluorescent lighting with the convenience and popularity of incandescent fixtures. CFLs fit most fixtures designed for incandescent bulbs and use about 75% less energy.

Although CFLs cost a bit more than comparable incandescent bulbs, they last 6–15 times as long (6,000–15,000 hours). See How Energy-Efficient Lightbulbs Compare with Traditional Incandescents, and find out how CFLs work.

CFLs are most cost-effective and efficient in areas where lights are on for long periods of time. You'll experience a slower payback in areas where lights are turned on for short periods of time, such as in closets and pantries. Because CFLs do not need to be changed often, they are ideal for hard-to-reach areas. Learn more about when to turn off your lights and replacing fluorescent lamps.

CFL Lighting

CFLs are available in a variety of styles or shapes, and each is designed for a specific purpose. The size or total surface area of the tube(s) determines how much light it produces. Many models are dimmable, as indicated on the package, and are and compatible with other lighting controls.

Common types of CFLs include:

• A-line and A-line spiral bulbs are screw-in base bulbs, and the most common; these can be used in common household fixtures that are designed for incandescent bulbs such as table lamps, ceiling fixtures, and wall sconces.
• Globe bulbs are similar to spiral bulbs, but feature a globe shape. These are used in more decorative fixtures where the bulb is visible such as bathroom and ceiling lighting.
• Floodlight and reflector bulbs also have a screw-in base, and are designed to focus light on the objects in front of them. They are commonly used in indoor fixtures such as recessed or canned lighting, and outdoor floodlights.
• Tubular bulbs can come with one to six tubes and feature a pin-based connection rather than a screw-in base. These bulbs are made to fit specific lighting fixtures.

Cleanup and Disposal

CFL bulbs contain a small amount of mercury, which is essential in conducting electricity in this type of bulb. Mercury can be hazardous to the environment, so it is important to recycle your used CFL bulbs rather than throw them away. Many hardware and other retail stores will recycle used CFL bulbs -- contact a local retailer to find out.

If a CFL bulb breaks, it can release some of its mercury as vapor. Therefore, you must follow specific cleanup steps to avoid coming in contact with the mercury. See the EPA recommendations for cleanup steps.

Fluorescent Tube and Circline Lighting

Fluorescent tubes -- the second most popular type of fluorescent lighting -- are more energy efficient than standard incandescent lightbulbs. 

The traditional tube-type fluorescent lights are usually identified as T12 or T8 (12/8 or 8/8 of an inch tube diameter, respectively). They are installed in dedicated fixtures with built-in ballasts. The two most common types are 40-watt, 4-foot (1.2-meter) lamps, and 75-watt, 8-foot (2.4-meter) lamps.

Tubular fluorescent fixtures and bulbs are often used for ambient lighting in large indoor areas. In these areas, their low brightness creates less direct glare than incandescent bulbs.

Circular, tube-type fluorescent lightbulbs are called circline bulbs. They are commonly used for portable task lighting.