Light dimmer circuit is used to control the lamp for arbitrary brightness. This dimmer circuit work for incandescent lamp, not a fluorescent one.  The dimmer circuit here work for both 110V and 220V AC.  Here is the schematic diagram of the circuit:

dimmer circuit schematic circuit schematic

Dimmer Wiring Diagram

The dimmer circuit is wired in series with the lamp, you can say the dimmer circuits is installed in series with the lamp. Be careful that the circuit is not isolated from high voltage, so the potentiometer should be installed with plastic knob.  Don’t touch the circuit or you’ll be shocked by the electricity.

Dimmer Control

The dimmer control is done by the potentiometer, you need to turn right or left to adjust the lamp’s brightness.

Dimmer Switch

The dimmer circuit has no switch, you can see only a fuse for safety. You can add a switch in series with the fuse, or just insert this dimmer circuit between the existing swith and the lamp. [Schematic diagram source: sprags.com]