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A semiconductor diode used to detect the presence of light or to measure its intensity. It usually consists of a pn junction device in a container that focuses any light in the environment close to the junction. The device is usually biased in reverse so that in the dark the current is small; when it is illuminated the current is proportional to the amount of light falling on it. See photoelectric cell; photoelectric effect.

Subjects: Astronomy and Astrophysics — Physics.

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