Photodetector

High Quality Content by WIKIPEDIA articles! Photosensors or photodetectors are sensors of light or other electromagnetic energy. There are several varieties:Optical detectors, which are mostly quantum devices in which an individual photon produces a discrete effect.Chemical detectors, such as photographic plates, in which a silver halide molecule is split into an atom of metallic silver and a halogen atom. The photographic developer causes adjacent molecules to split similarly.Photoresistors or Light Dependent Resistors (LDR) which change resistance according to light intensity.Photovoltaic cells or solar cells which produce a voltage and supply an electric current when illuminated.Photodiodes which can operate in photovoltaic mode or photoconductive mode.Photomultiplier tubes containing a photocathode which emits electrons when illuminated, the electrons are then amplified by a chain of dynodes.Phototubes containing a photocathode which emits electrons when illuminated, such that the tube conducts a current proportional to the light intensity.Phototransistors, which act like amplifying photodiodes.