Compact Fluorescent Light
How do CFL bulbs work?
Compact Fluorescent Lights or CFL's produce light differently than incandescent bulbs, in an incandescent electric current runs through a wire filament and heats the filament until it starts to glow. In a CFL, an electric current is driven through a tube containing argon and a small amount of mercury vapor. This generates invisible ultraviolet light that excites a fluorescent coating (called phosphor) on the inside of the tube, which then emits visible light.
CFL's need a little more energy when they are first turned on, but once the electricity starts moving, use about 75 percent less energy than incandescent bulbs. A CFL's ballast helps "kick start" the CFL and then regulates the current once the electricity starts flowing.
The entire process typically takes 30 seconds to 3 minutes to complete, which is why CFLs take longer than other lights to become fully lit. CFLs with decorative covers like globe or reflector shapes have a unique design challenge that results in the tradeoff of a slower warm up time, which is why these CFLs take longer than bare spirals to reach full brightness.
Older CFLs used large and heavy magnetic ballasts that caused a buzzing noise in some bulbs. Most CFLs today - and all ENERGY STAR qualified CFLs - use electronic ballasts, which do not buzz or hum.