Photocell

Information about Photocell

Photosensors or photodetectors are sensors of light or other electromagnetic energy. There are several varieties:

Most optical detectors are 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 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 cells, thermocouples and thermistors, 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 (Enss 2005).

In astronomy, the detecting devices generally used to record images are charge-coupled devices (CCD, a special semiconductor detector), although before the 1990s photographic plates were the most common. 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 discontinued producing several kinds of plates between 1980 and 2000, terminating the production of important sky surveys. See, for example, T. M. Girard et al, Astronomical Journal, 127, 3060 (May, 2004)[1]. The next generation of astronomical instruments (see for example Astro-E2) will include Cryogenic detectors. In experimental particle physics, a particle detector is a device used to track and identify elementary particles.

References

Enss, Christian (Editor) (2005). Cryogenic Particle Detection. Springer, Topics in applied physics 99. ISBN 3-540-20113-0.
Use of Photodetectors in lighting systems

sensor is a type of transducer. Direct-indicating sensors, for example, a mercury thermometer, are human-readable. Other sensors, such as a thermocouple, only produce an output voltage or other electrical output which must be interpreted by another device (such as a computer).
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Light is electromagnetic radiation of a wavelength that is visible to the eye (visible light). In a scientific context, the word "light" is sometimes used to refer to the entire electromagnetic spectrum.
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Electromagnetism is the physics of the electromagnetic field: a field which exerts a force on particles that possess the property of electric charge, and is in turn affected by the presence and motion of those particles.
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Optics (ὀπτική appearance or look in Ancient Greek) is a branch of physics that describes the behavior and properties of light and the interaction of light with matter.
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Photon

Photons emitted in a coherent beam from a laser
Composition: Elementary particle
Family: Boson
Group: Gauge boson
Interaction: Electromagnetic
Theorized: Albert Einstein (1905–17)
Symbol: or
Mass: 0^[1]
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Photographic plates were one of the earliest forms of photographic film, in which a light-sensitive emulsion of silver salts was applied to a glass plate. This form of photographic emulsion largely faded from the consumer market in the early years of the 20th century, as more
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A silver halide is one of the compounds formed between silver and one of the halogens — silver bromide (AgBr), chloride (AgCl) and iodide (AgI). As a group, they are often referred to as the silver halides, and are often given the pseudo-chemical notation AgX.
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In film developing, photographic developer (or just developer) is a chemical that makes the latent image on the film or print visible. It does this by reducing the silver halides that have been exposed to light to metals of elemental silver in the gelatine matrix.
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photoresistor or LDR is an electronic component whose resistance decreases with increasing incident light intensity. It can also be referred to as a light-dependent resistor (LDR), photoconductor, or photocell.
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Electrical resistance is a measure of the degree to which an object opposes an electric current through it. The SI unit of electrical resistance is the ohm. Its reciprocal quantity is electrical conductance measured in siemens.
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Photovoltaics, or PV for short, is a solar power technology that uses solar cells or solar photovoltaic arrays to convert light from the sun directly into electricity.
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A solar cell or photovoltaic cell is a device that converts light energy into electrical energy. Sometimes the term solar cell is reserved for devices intended specifically to capture energy from sunlight, while the term photovoltaic cell
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Voltage (sometimes also called electric potential difference or electrical tension) is the potential similarity of electrical potential between two points of an electrical or electronic circuit, expressed in volts.
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Electric current is the flow (movement) of electric charge. The SI unit of electric current is the ampere (A), which is equal to a flow of one coulomb of charge per second.

Definition

The amount of electric current (measured in amperes) through some surface, e.g.
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photodiode is a semiconductor diode that functions as a photodetector. Photodiodes are packaged with either a window or optical fibre connection, in order to let in the light to the sensitive part of the device. They may also be used without a window to detect vacuum UV or X-rays.
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Photoconductivity is an optical and electrical phenomenon in which a material becomes more conductive due to the absorption of electro-magnetic radiation such as visible light, ultraviolet light, infrared light,or gamma radiation.
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Photomultiplier tubes (photomultipliers or PMTs for short) are extremely sensitive detectors of light in the ultraviolet, visible and near infrared. These detectors multiply the signal produced by incident light by as much as 10⁸
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In a photomultiplier or Phototube, a photocathode is a negatively charged electrode coated with a photosensitive compound. When this is struck by light, electrons are emitted due to the photoelectric effect.
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Electron

Theoretical estimates of the electron density for the first few hydrogen atom electron orbitals shown as cross-sections with color-coded probability density
Composition: Elementary particle
Family: Fermion
Group: Lepton
Generation: First
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A dynode is one of a series of electrodes within a photomultiplier tube. Each dynode is more positively charged than its predecessor. Secondary emission occurs at the surface of each dynode.
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A phototube is a type of gas-filled or vacuum tube that is sensitive to light. These devices operate according to the photoelectric effect: incoming photons strike a photocathode, generating electrons, which are attracted toward the anode.
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Pyroelectricity is the ability of certain materials to generate an electrical potential when they are heated or cooled. As a result of this change in temperature, positive and negative charges move to opposite ends through migration (i.e.
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A Golay Cell, or Golay Detector, is a type of radiometer in which light is absorbed onto a plate in contact with a gas chamber, which heats the gas and causes it to expand against a diaphragm.
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In electronics, thermocouples are a widely used type of temperature sensor and can also be used as a means to convert thermal potential difference into electric potential difference.
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thermistor is a type of resistor used to measure temperature changes, relying on the change in its resistance with changing temperature. The word is a combination of thermal and resistor. Samuel Ruben invented the thermistor in 1930, and was awarded U.S. Patent No.
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Astronomy is the scientific study of celestial objects (such as stars, planets, comets, and galaxies) and phenomena that originate outside the Earth's atmosphere (such as the cosmic background radiation).
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charge-coupled device (CCD) is an analog shift register, enabling analog signals (electric charges) to be transported through successive stages (capacitors) controlled by a clock signal.
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