Dimmer switches detect the brightness of their surroundings by means of light-dependent resistance. As soon as illumination exceeds or falls below a set level, the resistance value changes. This causes the switching of an electrical contact, turning a light on or off, for example. The advantage of special dimmer switches is that they do not react to brief illumination such as that produced by lightning of headlights. Dimmer switches are often used outdoors in applications such as street lights.