A glass enclosure in which light is produced when electricity is passed through mercury vapor inside the enclosure.

The electricity 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 room, comes in many differently-shaped configurations, and is designed to be used in some fixtures originally intended to hold incandescent lamps.

A glass enclosure in which light is produced when a tungsten filament is electrically heated so that it glows.

Much of the energy is converted into heat; therefore, this class of lamp is a relatively inefficient source of light.

Included in this category are the familiar screw-in light bulbs, as well as somewhat more efficient lamps, such as tungsten halogen lamps, reflector or r-lamps, parabolic aluminized reflector (PAR) lamps, and ellipsoidal reflector (ER) lamps.

A type of high-intensity discharge (HID) lamp in which most of the light is produced by radiation of metal halide (chemical compound of a halogen) and mercury vapors in the arc tube, similar in construction and appearance to mercury vapor lamps.

The addition of metal halide gases results in higher light output, more lumens (unit of luminous flux) per watt, and better color rendition than from mercury gas alone.