Fluorescent lamps use 25%-35% of the energy used by incandescent lamps to provide the same amount of illumination (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 lamps 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 needed to allow dimming of fluorescent lamps.
Compact Fluorescent Lamps
Compact fluorescent lamps (CFLs) combine the energy efficiency of fluorescent lighting with the convenience and popularity of incandescent fixtures.
CFLs can replace incandescents that are roughly 3-4 times their wattage, saving up to 75% of the initial lighting energy. Although CFLs cost 3-10 times more than comparable incandescent bulbs, they last 6-15 times as long (6,000-15,000 hours).
CFLs work much like standard fluorescent lamps. They consist of two parts: a gas-filled tube and a magnetic or electronic ballast. The gas in the tube glows with ultraviolet light when electricity from the ballast flows through it. This, in turn, excites a white phosphor coating on the inside of the tube, which emits visible light throughout the surface of the tube.
CFLs with magnetic ballasts flicker slightly when they start. They are also heavier than those with electronic ballasts. This may make them too heavy for some light fixtures. Electronic ballasts are more expensive but light immediately (especially at low temperatures). They are also more efficient than magnetic ballasts. The tubes will last about 10,000 hours and the ballast about 50,000 hours. Most currently available CFLs have electronic ballasts.
CFLs are designed to operate within a specific temperature range. Temperatures below the range cause reduced output. Most are for indoor use, but there are models available for outdoor use. A CFL's temperature range is usually listed on its package.
CFLs are most cost-effective and efficient in areas where lights are on for long periods of time. Because CFLs do not need to be changed often, they are ideal for hard-to-reach areas.
Types of Compact Fluorescent Lamps
CFLs are available in a variety of styles and shapes. They may have two, four, or six tubes or circular or spiral-shaped tubes. The size or total surface area of the tube(s) determines how much light is produced.
In some CFLs, the tubes and ballast are permanently connected. Other CFLs have separate tubes and ballasts. This allows the tubes to be changed without changing the ballast. There are also types enclosed in a glass globe. These look somewhat similar to conventional incandescent light bulbs, except they are larger.
Sub-CFLs fit most fixtures designed for incandescent lamps. Although most CFLs fit into existing three-way light sockets, only a few special CFL models can be dimmed.
Fluorescent Tube and Circline Lamps
Fluorescent tube lamps—the second most popular type of lamps—are more energy efficient than the more popular A-type standard incandescent lamps.
The traditional tube-type fluorescent lamps are usually identified as T12 or T8 (twelve-eighths or eight-eighths of an inch tube diameter, respectively). They are installed in a dedicated fixture with a built-in ballast. 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 lamps are preferred for ambient lighting in large indoor areas. In these areas, their low brightness creates less direct glare than incandescent bulbs.
Circular tube-type fluorescent lamps are called circline lamps. They are commonly used for portable task lighting.