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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 ?
We can record exactly when the path of the laser has been broken because of the voltage change in the circuit due to the resistance change of the photoresistor. The change in voltage also influences a second circuit wired to an LED bulb.
This lower SBB requires a lower [N.sub.F], which leads to a lower W, thus increasing the channel cross-section of the photoresistor and hence its conductance.
The firm succeeded in commercializing the photoresistor and coating materials for optical fibers in 1982.
Current parameter not being the only reason, but also the voltage generation which was not like the photoresistors, which became a point for the selection of phototransistors over others.
Particularly, commercial LEDs produce fluctuations, and commercial photoresistors delay change detection, of light intensity.
Due to its desirable properties, it finds use in photovoltaic solar cells [2, 3], piezo transducers [4], photoresistors, luminescence devices [5], Schottky diodes and metal-semiconductor field effect transistors (MESFETs) [6], heterojunction diodes [7], insulated gate thin film transistors [8], and gas sensors [9].
The mechanism for detecting the position of the sun consists of an arrangement of two connected photoresistors as shown in Figure 4.
--photon (photoelectric)--photoconductive (photoresistors), photovoltaic (photodiodes), on QWJP quantum wells (Quantum Well Infrared Photodetector).