A sensor light is an electronic device that is used to detect light. It consists of a photocell or photo resistor, a charged couple device (CCD) and photomultipliers. When light shines on the photocell or photo resistor, the resistance of the device changes and it causes the CCD to transport electrically charged signals which turns the light on. Photomultipliers aid the process by multiplying light when it is detected. Some sensor lights utilise body heat and wave lengths to detect movement. These lights should be used because they help in saving electricity and are also very reliable.