Electrical dimmer switches allow you to manage the level of light in a room by turning a dial instead of clicking a standard on and off switch. The dimmer mechanism regulates the amount of electricity flowing through the circuit when the dial is turned clockwise or counter-clockwise, increasing or decreasing the level of light. A standard U.K. light switch can be replaced with a dimmer switch, but be aware that dimmers are not suitable for use with fluorescent bulbs.
Switch off the electricity supply at the mains, or breaker. This is extremely important because you will be dealing with live wires during the installation process.
Remove the two screws on the cover plate. Pull the plate away from the wall so you can access the internal wiring comfortably.
Check to see if there is an additional green and yellow wire. If you are removing a metal face plate, you will find a short green and yellow earth, or ground, wire running between a small terminal and the metal pattress box in the wall. A plastic face plate does not have an earth wire.
Make a note of the terminal that each colour coded wire is attached to before you remove it so that you can match the wires of the new dimmer switch accordingly.
Unscrew the wires from each terminal and reconnect the dimmer switch in the same way the original light switch was connected.
Push the dimmer unit against the pattress box until it clicks into place. Secure the dimmer face plate to the box with the supplied screws.
Turn on the electricity supply at the mains or breaker and test the dimmer switch by turning the dial clockwise to increase the level of light and counter-clockwise to decrease the light.
If your original light switch has other wires in addition to the red, black and earth, you should consult an electrician because it is probably a two-way switch. These can be operated from more than one location and have extra wires that should be replaced only by a professional.