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McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


A device that detects light. Used for photographic light meters, automatic on-at-dusk street lights and other light-sensitive applications, a photocell varies its resistance between its two terminals based on the amount of photons (light) it receives. Also called a "photodetector," "photoresistor" and "light dependent resistor" (LDR).

The photocell's semiconductor material is typically cadmium sulfide (CdS), but other elements are also used. Photocells and photodiodes are used for similar applications; however, the photocell passes current bi-directionally, whereas the photodiode is unidirectional. See photodiode.

Light Dependent Resistors
Photocells come in a variety of packages such as this assortment from PerkinElmer. As the photocell receives more photons, the resistance is lowered between the two terminals. (Image courtesy of PerkinElmer, Inc.,
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References in periodicals archive ?
Qi, "Implementation of an analogue model of a memristor based on a light-dependent resistor," Chinese Physics B, vol.
A light-dependent resistor (LDR) is a photoconductive sensor commonly used in devices that create an action depending on the presence or lack of light, as determined by the changes its electrical resistance.
In order to track the position of the sun accurately, there are four light-dependent resistor sensors (LDR sensors, NSL19-M51 RS, an electro components company, Northants) to identify the intensity of the sunlight.