A fluorescent lamp or fluorescent tube is a gas-discharge lamp that uses electricity to excite mercury vapor. The excited mercury atoms produce short-wave ultraviolet light that then causes a phosphor to fluoresce, producing visible light. A fluorescent lamp converts electrical power into useful light more efficiently than an incandescent lamp. Lower energy cost typically offsets the higher initial cost of the lamp. The lamp is more costly because it requires a ballast to regulate the flow of current through the lamp.
While larger fluorescent lamps have been mostly used in commercial or institutional buildings, the compact fluorescent lamp is now being used as an energy-saving alternative to incandescent lamps in homes. Compared with incandescent lamps, fluorescent lamps last longer, but are bulkier, more complex, contain trace amounts of mercury, and have poorer color rendition.