A dimmer switch gives you the ability to either automatically or manually adjust the brightness of the light fixture or fixtures that it is connected to. There are four basic styles of dimmer switches on the market today. Among them are rotary, also called dial-type, slide-action, toggle, and automatic dimmers. They all adjust the lighting connected to them and can set the brightness from very dim, almost a moonlight effect, to full brightness. These switches can replace a single-pole switch connected to lighting circuits. It is even possible to place three-way dimmers on a circuit, but these dimmers should be bought in a packaged pair labeled for three-way switching installation. That way, they are sure to work together.
Dimmer switches are bulkier than standard single-pole switches. They have an aluminum face that helps dissipate the heat they generate. For this reason, dimmer switches should be placed in junction boxes that are large enough to accomodate not only the switch, but also the wiring connected to it.
Unlike standard switches that employ terminal screws to make the electrical connections, dimmer switches have wire leads to connect the switch to the circuit. These wires are both black wires for the hot feed and the switch leg connection. In some cases a third wire (green) will be attached for a ground connection.