Editing Photoresistor (section)

==Applications==
[[Image:Streetlight control.jpg|thumb|The internal components of a photoelectric control for a typical USA [[streetlight]]. The photoresistor is facing rightwards and controls whether current flows through the heater which opens the main power contacts. At night, the heater cools, closing the power contacts, energizing the street light.]]

Photoresistors come in many types. Inexpensive [[cadmium sulfide]] (CdS) cells can be found in many consumer items such as camera light meters, clock radios, [[alarm devices]] (as the detector for a light beam), [[nightlight]]s, outdoor clocks, solar street lamps, and solar road studs, etc.

Photoresistors can be placed in streetlights to control when the light is on. Ambient light falling on the photoresistor causes the streetlight to turn off. Thus energy is saved by ensuring the light is only on during hours of darkness.

Photoresistors are also used in laser-based security systems to detect the change in the light intensity when a person or object passes through the laser beam.

They are also used in some [[Dynamic range compression|dynamic compressors]] together with a small [[incandescent lamp|incandescent]] or [[neon lamp]], or [[light-emitting diode]] to control gain reduction. A common usage of this application can be found in many [[guitar amplifiers]] that incorporate an onboard [[Tremolo (electronic effect)|tremolo]] effect, as the oscillating light patterns control the level of signal running through the amplifier circuit.

The use of CdS and [[Cadmium selenide|CdSe]]<ref>{{cite web |title=Silonex: ''TO-18 photocells on ceramic substrate'' |url=http://www.silonex.com/datasheets/specs/images/pdf/102899.pdf |format=PDF |access-date=17 October 2013 |url-status=dead |archive-url=https://web.archive.org/web/20130401053725/http://www.silonex.com/datasheets/specs/images/pdf/102899.pdf |archive-date=1 April 2013 }}</ref> photoresistors is severely restricted in Europe due to the [[Restriction of Hazardous Substances Directive|RoHS]] ban on [[cadmium]].

[[Lead(II) sulfide|Lead sulfide]] (PbS) and [[indium antimonide]] (InSb) LDRs (light-dependent resistors) are used for the mid-infrared spectral region. [[germanium|Ge]]:[[copper|Cu]] photoconductors are among the best far-[[infrared]] detectors available, and are used for [[infrared astronomy]] and [[infrared spectroscopy]].