A light Dimmer is a electronic circuit which permits the gradual dimming of lights. It is similar to a domestic fan regulator.
Dimmers are usually powered by a TRIAC (See article on TRIAC). The TRIAC does not conduct for the full cycle. It switches the light on only for part of the waveform. The firing angle of the TRIAC is controlled by an external potentiometer.
Light dimmers are used widely in domestic and industrial lighting, in aircraft, etc. Light Dimmers can be used with incandescent lamps, Light Emitting Diodes, and compact fluorescent lamps.