A dimmer is a device connected to a light fixture and used to lower the brightness of the light. By changing the voltage waveform applied to the lamp, it is possible to lower the intensity of the light output. Dimmers add longevity to your light bulbs by lowering the amount of time your light bulbs are at the highest point of energy exertion. Using dimmers on a softer lighting setting can give an extra 3 or 4 years of usage of your light bulbs. This means that you will not have to replace your bulbs as often.