When choosing a dimmer switch, you should first check it is compatible with your lighting set-up and choice of bulbs. You should then decide which style is best for you and whether you want to pay extra to avoid unwelcome side effects such as buzzing and radio interference. Finally you must make sure the dimmer switch has a sufficient wattage rating for the lights you will use it with.
A dimmer switch works by modifying the way lights are powered by an alternating current, or AC. This means the voltage continually rises and falls in a consistent pattern. A dimmer switch will cut off the light bulb circuit every time the pattern changes direction. The higher the switch is set, the quicker it turns the circuit back on. This changes the amount of energy supplied to the bulb, and thus the brightness of the light.
Most dimmer switches are not compatible with energy saving light bulbs. That's because such bulbs work in a different way to ordinary filament bulbs. An energy saving bulb contains glass tubes coated in phosphor. When electricity passes through these bulbs, the gas gives out ultraviolet rays which light up the phosphor. When used with a dimmer switch, these bulbs simply flicker on and off. While there are efforts to solve this problem, for now the closest solution is to use switches which let you choose from two or three fixed levels of brightness.
There are three main styles of dimmer switch. The most common is the type with a rotating switch which, rather than simply having on and off settings, lets the user turn the dial to gradually change the brightness of the bulb. Another type is a touch dimmer where the user simply touches a plate. This can work like a switch to cycle through several pre-set levels of brightness. Alternatively, the user can press down while the bulb gradually increases or decreases in brightness and then letting go once they reach their preferred setting. A third style involves a remote control, sometimes controlling two or more different sets of lights.
The cheapest dimmer switch is not always the best option. This is because the rapid changes in the voltage supplied to the bulb can cause excessive vibrations in its filament, which makes a potentially-annoying buzzing sound. Because the filament is magnetic, this effect can also cause some interference to nearby televisions and radios. Better quality dimmer switches will include devices known as inductor chokes or interference capacitors. These can smooth out the effects of the changing voltage and thus remove the buzzing sound.
Each dimmer switch comes with a wattage rating. This tells you the maximum watts of bulbs you can control with it. This is not simply advice, but rather an important limit to follow as breaching it can risk serious damage. Pay particular attention to set-ups where you will be controlling multiple bulbs from one switch. You will need to add up the wattage of each and every bulb concerned.