|Cadmium sulfide photoresistor.|
The s-curve on this sensor is made of cadmium sulfide, a semiconductor that becomes significantly more conductive to electricity when it is exposed to light. The sensor is wired in series with a wire coil wrapped around a bi-metallic strip. In the dark, little current flows through the circuit, and the wire coil remains cold. When exposed to light, the resistance drops, current flow increases, and the wire coil heats up the bi-metallic strip, causing it to bend, which in turn snaps a relay contact to the opposite position. This is a daylight sensor designed to turn an outdoor lamp on at dusk and off at dawn.
Source: Farm & Fleet
Contributor: Theodore Gray
Acquired: 22 April, 2009
Text Updated: 23 April, 2009