Not only do dimmers save energy, but they also help create a romantic mood in any room. Changing a simple light switch to a dimmer is easy.
Determine the nature of the light you want to dim. If it's a simple incandescent light, you are in luck. If you've upgraded your lighting to florescent lighting or light-emitting diodes (LEDs), they probably won't work with a dimmer, so swap the bulb back.
Determine the wattage of the light that your dimmer will control. Then measure the size of the fixture you are about to replace. Decide if you will replace the entire faceplate or just the switch itself. Note if the switch is a single pole, the only one controlling the light, or a double pole, where the light is controlled by two switches.
Buy an appropriate replacement at your local hardware store. Have the screwdriver that you need for the work at hand.
Find the circuit breakers for the switch that you want to change out. Leave the desired light on and flip each of the breakers in your breaker box until it goes off.
Mark the breaker with a note that the switch should be left off, because maintenance is in progress. You don't want to change this fixture while it is hot. More people get electrocuted each year from 120-volt house current than from the high voltages used to shuttle electricity around the grid.
Unscrew the screws attaching the fixture to the wall. Gently pull it from the wall. Pay particular attention to how it is wired. If it is a double pole, one of the wires will have a label that reads "common." You must attach this to the same point in your replacement dimmer, so label it when you remove this wire. Remove the wires by unscrewing the screws and unwrapping the wires.
Look at the dimmer. A single pole will have two black wires with a green grounding wire. A double pole has two red wires, a green and a black. Wrap the green ground wire to the grounding screw in the fixture or to its green wire. Screw in the screw.
For a single pole, wrap and attach the two black wires, then drive in the screws.
For a double pole, attach the two red wires, with the black one to the point labelled "common." Make sure that all the connections are held by wiring nuts, although it is possible to simply knot the connections and secure them with electrical tape. In no cases should any raw wire touch another or part of the dimmer, which can cause a short circuit.
With your screwdriver, replace the screws and mounting plate. Restore the power.
Remember when it comes to screws, "righty tighty, lefty loosey."