Lamp in which the light is produced by electrical discharge through gases or metal vapours. A distinction is drawn between low-pressure and high-pressure discharge lamps. Low-pressure discharge lamps include conventional fluorescent lamps and compact fluorescent lamps. Their light is produced by exciting the fluorescent substances with radiation. High-pressure discharge lamps include mercury vapour lamps, Halogen-metal halide lamps and high-pressure sodium vapour lamps. Their light spectrum is due to their unique composition and high operating pressure.