Photoelectric cell.

An electrical device which is sensitive to light. Selenium and cadmium sulfide (CdS) cells were both used in old-fashioned light meters, though they work on slightly different principles.

Selenium cells generate electricity when light falls on them, and this electricity can be used to move a needle. However they aren’t very useful at low light levels when the cell can’t generate enough power. CdS cells, on the other hand, vary in electrical resistance when light falls on them. So a light meter with a CdS cell requires a small battery in order to operate, but can work at much lower light levels than a selenium cell. CdS cells have poor red sensitivity, however.

Modern cameras often use silicon photoelectric cells for light metering.

cf. light meter, SPC.

Entry last updated 2002-04-03. Term 908 of 1487.

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