Fluorescent light bulbs are lamps that use the phenomena of fluorescence to produce light. Fluorescence is the emission of radiation by a substance that is exposed to an external source of radiation. They are much more efficient than traditional incandescent bulbs, since incandescent bulbs waste most of their energy producing heat rather than light.
Fluorescent bulbs consist of glass tubes filled with low pressure mercury-argon vapor. The inner wall of the tube is coated with a white phosphor. A heated filament emits electrons into the vapor, causing the vapor atoms to emit ultraviolet light. This ultraviolet light is then absorbed by the white phosphor and re-emitted as visible light.