A device that regulates or produces a current or voltage in response to certain types of radiation, especially visible light. It is gernerally based on a semiconductor, such as selenium, germanium, or silicon, suitably prepared or modified.

In a photoemissive cell, a photosensitive cathode emits electrons when it is illuminated. These electrons constitute a current when they flow to the positive anode of a cell. In a photovoltaic cell, light changes the behavior of a p-n junction (a certain conductive junction between certain layers of a semiconductor), creating an electric potential difference by the photovoltaic effect. In a photoconductive cell, the resistance of a substance changes as a result of photoconductivity. Photoelectric cells are used in light meters, as in photography; light detectors, as in burglar alarms; and spacecraft power supplies.

Also called: photocell
See also: photoelectric effect

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