Photodetector

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• Optical
  Optics
  
  Optics is the study of the behavior and properties of light including its optical phenomena with matter and its imaging by optical instruments....
   detectors, which are mostly quantum devices in which an individual photon
  Photon
  
  In physics, the photon is an elementary particle, the quantum of the electromagnetic field and the basic unit of light and all other forms of electromagnetic radiation....
   produces a discrete effect.

• Chemical detectors, such as photographic plate
  Photographic plate
  
  Photographic plates preceded photographic film as a mean of photography. A light-sensitive emulsion of silver salts was applied to a glass plate....
  s, in which a silver halide
  Silver halide
  
  A silver halide is one of the Chemical compound formed between silver and one of the halogens — silver bromide , silver chloride , silver iodide , and two forms of silver fluorides....
   molecule is split into an atom of metallic silver and a halogen atom. The photographic developer
  Photographic developer
  
  In the Photographic processing, plates or papers, the photographic developer is a chemical that makes the latent image on the film or print visible....
   causes adjacent molecules to split similarly.

• Photoresistor
  Photoresistor
  
  A photoresistor or light dependent resistor or cadmium sulfide cell is a resistor whose electrical resistance decreases with increasing incident light intensity....
  s or Light Dependent Resistors (LDR) which change resistance
  Electrical resistance
  
  The electrical resistance of an object is a measure of its opposition to the passage of a steady electrical current. An object of uniform cross section will have a resistance proportional to its length and inversely proportional to its cross-sectional area, and proportional to the resistivity of the material....
   according to light intensity

• Photovoltaic cells or solar cell
  Solar cell
  
  A solar cell or photovoltaic cell is a device that converts sunlight directly into electricity by the photovoltaic effect. Sometimes the term solar cell is reserved for devices intended specifically to capture energy from sunlight, while the term photovoltaic cell is used when the source is unspecified....
  s which produce a voltage
  Voltage
  
  Electrical tension is the potential difference between two points of an electrical or electronic circuit, expressed in volts. It is the measurement of the potential for an electric field to cause an electric current in an electrical conductor....
   and supply an electric current
  Electric current
  
  Electric current is the flow of electric charge. The electric charge may be either electrons or ions.The International System of Units unit of electric current intensity is the ampere....
   when illuminated

• Photodiode
  Photodiode
  
  A photodiode is a type of photodetector capable of converting light into either electric current or voltage, depending upon the mode of operation....
  s which can operate in photovoltaic mode or photoconductive mode

• Photomultiplier
  Photomultiplier
  
  Photomultiplier tubes , members of the class of vacuum tubes, and more specifically phototubes, are extremely sensitive detectors of light in the ultraviolet, visible light, and near-infrared ranges of the electromagnetic spectrum....
   tubes containing a photocathode
  Photocathode
  
  A photocathode is a negatively charged electrode in a light detection device such as a photomultiplier or phototube that is coated with a photosensitive compound....
   which emits electron
  Electron
  
  The electron is a subatomic particle that carries a negative electric charge. It has elementary particle and is believed to be a point particle....
  s when illuminated, the electrons are then amplified by a chain of dynode
  Dynode
  
  A dynode is one of a series of electrodes within a photomultiplier tube. Each dynode is at a more positive electrical potential than its predecessor....
  s.

• Phototube
  Phototube
  
  A phototube is a type of gas filled tube or vacuum tube that is extremely sensitive to light in the ultraviolet, visible light, and near-infrared ranges of the electromagnetic spectrum....
  s containing a photocathode
  Photocathode
  
  A photocathode is a negatively charged electrode in a light detection device such as a photomultiplier or phototube that is coated with a photosensitive compound....
   which emits electron
  Electron
  
  The electron is a subatomic particle that carries a negative electric charge. It has elementary particle and is believed to be a point particle....
  s when illuminated and in general behaves as a photoresistor.

• Phototransistors incorporating one of the above sensing methods

• Optical detectors that are effectively thermometers, responding purely to the heating effect of the incoming radiation, such as pyroelectric detectors, Golay cell
  Golay Cell
  
  A Golay Cell, or Golay Detector is a type of detector mainly used for infrared spectroscopy. It consists of a small metal cylinder which is closed by a blackened metal plate at one end and by a flexible metalized diaphragm at the other....
  s, thermocouple
  Thermocouple
  
  A thermocouple is a junction between two different metals that produces a voltage related to a temperature difference. Thermocouples are a widely used type of list of temperature sensors and can also be used to convert heat into electric power....
  s and thermistor
  Thermistor
  
  A thermistor is a type of resistor with electrical resistance proportional to its temperature. The word is a portmanteau of Thermal and resistor....
  s, but the latter two are much less sensitive.

• Cryogenic detectors are sufficiently sensitive to measure the energy of single x-ray, visible and near infra-red photons.

• Charge-coupled device
  Charge-coupled device
  
  A charge-coupled device is an analog signal shift register that enables the transportation of analog signals through successive stages , controlled by a clock signal....
  s (CCD), which are used to record images in astronomy
  Astronomy
  
  Astronomy is the science of Astronomical object and Phenomenon that originate outside the Earth's atmosphere . It is concerned with the evolution, physics, chemistry, meteorology, and motion of celestial objects, as well as the physical cosmology....
  , digital photography
  Digital photography
  
  Digital photography is a form of photography that utilizes digital technology to make s of subjects. Until the advent of such technology, photography used photographic film to create images which could be made visible by photographic processing....
  , and digital cinematography
  Digital cinematography
  
  Digital cinematography is the process of capturing motion pictures as digital images, rather than on photographic film. Digital capture may occur on Video tape, hard drives, flash memory, or other media which can record digital data....
  . Although before the 1990s photographic plate
  Photographic plate
  
  Photographic plates preceded photographic film as a mean of photography. A light-sensitive emulsion of silver salts was applied to a glass plate....
  s were the most common in astronomy. Glass-backed plates were used rather than film, because they do not shrink or deform in going between wet and dry condition, or under other disturbances. Unfortunately, Kodak
  Eastman Kodak
  
  Eastman Kodak Company is a multinational corporation public company which produces imaging and photography materials and equipment. Long known for its wide range of photographic film products, Kodak is re-focusing on two major markets: digital photography and digital printing....
   discontinued producing several kinds of plates between 1980 and 2000, terminating the production of important sky surveys. The next generation of astronomical instruments, such as the Astro-E2, include cryogenic detectors. In experimental particle physics
  Particle physics
  
  Particle physics is a branch of physics that studies the elementary particle constituents of matter and radiation, and the interactions between them....
  , a particle detector
  Particle detector
  
  In experimental and applied particle physics and nuclear engineering, a particle detector, also known as a radiation detector, is a device used to detect, track, and/or identify high-energy Elementary particles, such as those produced by nuclear decay, cosmic radiation, or reactions in a particle accelerator....
   is a device used to track and identify elementary particles.

• LEDs reverse-biased to act as photodiodes. See LEDs as Photodiode Light Sensors.

See also

• List of sensors
  List of sensors
  
  * Accelerometer* Active pixel sensor* Air flow meter* Alarm sensor* Bedwetting alarm* Bhangmeter* Biochip* Biosensor* Breathalyzer* Capacitance probe...