CFL is the abbreviation of Compact Fluorescent Lamp. In a CFL, an electric current is passed through a glass tube containing argon and a small amount of mercury vapour. This generates invisible UV light that excites a fluorescent coating (called phosphor) on the inside of the tube. This then emits visible light. CFL needs a little more energy when it is first turned on, but once electricity starts moving through it, CFLs consume approximately 70% less energy than the conventional incandescent (i.e. filament-type) lamp.