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.