Lights use power only when they are turned on. The use of sensors to trigger power flow to the light is a way to control the supply of power to a light fixture so that the light is on only under the desired conditions. Using sensors to detect light levels keeps power from reaching the lights until it becomes dark enough for the sensor to react and activate the fixture only when light is needed. This reduces the power required to operate the light. This can be very important in saving energy in exterior security lights, interior lighting, and landscaping lights. Motion-activated lights save power by the same basic principle. The sensors, however, detect motion within a given radius and activate the lights only when some movement is detected. Over a period of years, using motion-activated lighting fixtures can save a good amount of power in garden lights, security lights, and interior lighting. For example, the installation of a motion sensor in a laundry room will turn the light on or off as someone enters the room. For some families, this ends the struggle to remind children to turn lights off when they leave a room.

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