Dimmers are devices connected to a light fixture and used to lower the brightness of light. By changing the voltage waveform applied to the lamp, it is possible to lower the intensity of the light output. Although the term dimmer is generally reserved for those intended to control light output from resistive incandescent, halogen, and compact fluorescent lights (LEDs).
Dimmers range in size from small units the size of domestic light switches to high-power units used in large theatrical or architectural lighting installations. In the professional lighting industry, changes in intensity are called “fades” and can be “fade up” or “fade down”. Dimmers with direct manual control had a limit on the speed that varied but this problem has been largely eliminated with modern digital units.