Discharge lamps generate light by sending an electrical discharge through an ionised gas or metal vapour. Depending on the gas with which a lamp is filled, it either radiates visible light directly or converts UV radiation to light through interaction with a fluorescent coating on the inside surface of the glass enclosure. The operating pressure inside a discharge lamp is either low (low pressure discharge lamps) or high (high-pressure discharge lamps). Examples include:

• Low-pressure discharge lamps: linear fluorescent lamps, compact fluorescent lamps and energy-saving lamps, induction lamps, low-pressure sodium lamps
• High-pressure discharge lamps: metal halid lamps and high-pressure sodium vapour lamps