A glass enclosure in which light is produced when electricity is passed through mercury vapor inside the enclosure: The electricity in a fluorescent lamp creates a radiation discharge that strikes a coating on the inside surface of the enclosure, causing the coating to glow.

Traditional fluorescent lamps are usually straight or circular white glass tubes used in fixtures specially designed for them.

A newer type of fluorescent lamp, the compact fluorescent lamp, takes up much less space, comes in many differently-shaped configurations, and is designed to be used in some fixtures originally intended to hold incandescent lamps.