A fluorescent lamp, or fluorescent
tube, is a low-pressure mercury-vapor gas-discharge lamp that
uses fluorescence to produce visible light. An electric current in the gas
excites mercury vapor, which produces short-wave ultraviolet light that
then causes a phosphor coating on the inside of the lamp to glow.
A
fluorescent lamp converts electrical energy into useful light much more
efficiently than an incandescent lamp. The typical luminous efficacy of
fluorescent lighting systems is 50–100 lumens per watt, several times the
efficacy of incandescent bulbs with comparable light output. For comparison,
the luminous efficacy of an incandescent bulb may only be 16 lumens per watt.
Fluorescent lamp fixtures are more costly than incandescent
lamps because, among other things, they require a ballast to regulate
current through the lamp, but the initial cost is offset by a much lower
running cost. Compact fluorescent lamps are now available in the same popular
sizes as incandescent and are used as an energy-saving alternative in
homes.
