(Redirected from Photoresistor)

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A photocell, also known as a photoresistor, photoconductor, light dependant resistor (LDR), or cadmium sulfide (CdS) cell, is a resistor while resistance varies according to light intensity.

Photocells are inexpendive light detectors with a slow rate of light detection, making them ideal for many comsumer applications such as camera light meters and street lamps.

Photocells are typically cadmium sulfide cells, but some specialty applications may use different sensors, such as Lead sulfide (PbS) and indium antimonide (InSb) sensors for the mid-infrared spectral region, and germanium copper (GeCu) photocells for the far-infrared spectral region.


Technical Details

A photoresistor is made from a high-resistance semi-conductor whose face is exposed to light. Light of high enough frequency causes photons of the semi-conductor to give off electrons, causing the semi-conductor to switch into the conductor band, thus changing its overall resistance.

Photocells do not provide linear voltage in respect to the amount of light.


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