To control the light for arbitrary brightness, this circuit diagram will be suitable. This circuit work for incandescent lamp and not for the fluorescent lamp. It also works for 110 and 220V AC. Here is the circuit diagram :

light dimmer schematic diagram

light dimmer circuit diagram

The dimmer circuit is installed series with the lamp. Take note that this schematic is not isolated from high voltage, therefore the potentiometer should be installed with plastic knob. Don’t touch the circuit, it will shock you.

The control of the dimmer is done by the potentiometer. You can adjust the brightness by turning it into the left/right.

This circuit doesn’t have any switch. For safety, there is a fuse only. Switch can be added in series with the fuse, or insert this dimmer circuit between the lamp and existing switch.

[Source : sprags.com]