 The internal components of a photoelectric control for a typical American 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. The heater/bimetal mechanism provides a built-in time-delay. A 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. Image File history File links LDR.jpg Summary source: nl:user:BenTheWikiMan info: 139x486 (10876 bytes) (LDR, lichtgevoelige weerstand, eigen foto) LDR, lichtgevoelige weerstand, eigen LDR, zelf ingescand. ...
Image File history File links LDR.jpg Summary source: nl:user:BenTheWikiMan info: 139x486 (10876 bytes) (LDR, lichtgevoelige weerstand, eigen foto) LDR, lichtgevoelige weerstand, eigen LDR, zelf ingescand. ...
Image File history File links Size of this preview: 757 × 600 pixelsFull resolution (1161 × 920 pixel, file size: 98 KB, MIME type: image/jpeg) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Photoresistor Street light ...
Image File history File links Size of this preview: 757 × 600 pixelsFull resolution (1161 × 920 pixel, file size: 98 KB, MIME type: image/jpeg) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Photoresistor Street light ...
A streetlight in front of a red sky at night A street light, also known as a light standard, is a raised light on the edge of a road, turned on or lit at a certain time every night. ...
Various components An electronic component is a basic electronic element usually packaged in a discrete form with two or more connecting leads or metallic pads. ...
Electrical resistance is a measure of the degree to which an electrical component opposes the passage of current. ...
A photoresistor is made of a high-resistance semiconductor. If light falling on the device is of high enough frequency, photons absorbed by the semiconductor give bound electrons enough energy to jump into the conduction band. The resulting free electron (and its hole partner) conduct electricity, thereby lowering resistance. A semiconductor is a solid whose electrical conductivity is in between that of a conductor and that of an insulator, and can be controlled over a wide range, either permanently or dynamically. ...
For other uses, see Frequency (disambiguation). ...
In modern physics the photon is the elementary particle responsible for electromagnetic phenomena. ...
For other uses, see Electron (disambiguation). ...
In semiconductors and insulators, the conduction band is the range of electron energy, higher than that of the valence band, sufficient to make the electrons free to accelerate under the influence of an applied electric field and thus constitute an electric current. ...
For the following two reasons the electron hole was introduced into calculations: If an electron is excited into higher state it leaves a hole in its old state. ...
Electrical resistance is a measure of the degree to which an electrical component opposes the passage of current. ...
A photoelectric device can be either intrinsic or extrinsic. An intrinsic semiconductor has its own charge carriers and is not an efficient semiconductor, eg. silicon. In intrinsic devices, the only available electrons are in the valence band, and hence the photon must have enough energy to excite the electron across the entire bandgap. Extrinsic devices have impurities added, which have a ground state energy closer to the conduction band — since the electrons don't have as far to jump, lower energy photons (i.e. longer wavelengths and lower frequencies) are sufficient to trigger the device. If a sample of silicon has some of its atoms replaced by phosphorus atoms(impurities), there will be extra electrons available for conduction. This is an example of an extrinsic semiconductor. In solids, the valence band is the highest range of electron energies where electrons are normally present at zero temperature. ...
In solid state physics and related applied fields, the band gap is the energy difference between the top of the valence band and the bottom of the conduction band in insulators and semiconductors. ...
Cadmium sulphide cells
Cadmium sulphide (CdS) cells rely on the material's ability to vary its resistance according to the amount of light striking the cell. The more light that strikes the cell, the lower the resistance. Although not accurate, even a simple CdS cell can have a wide range of resistance from less than 100 Ω in bright light to in excess of 10 MΩ in darkness. Many commercially available CdS cells have a peak sensitivity in the region of 500nm - 600nm (green light). The cells are also capable of reacting to a broad range of frequencies, including infrared (IR), visible light, and ultraviolet (UV). They are often found on street lights as automatic on/off switches. They were once even used in heat-seeking missiles to sense for targets. Cadmium sulfide, the mineral Greenockite, is an hexagonal, orange crystal with specific gravity of 4. ...
For other uses, see Infrared (disambiguation). ...
This article does not cite any references or sources. ...
For other uses, see Ultraviolet (disambiguation). ...
The AIM-9 Sidewinder is a heat-seeking, short-range, air-to-air missile carried by fighter aircraft and recently, certain gunship helicopters. ...
Applications Photoresistors come in many different types. Inexpensive cadmium sulphide cells can be found in many consumer items such as camera light meters, clock radios, security alarms, street lights and outdoor clocks. This article is about the photographing device. ...
A light meter is a device used to measure the amount of light. ...
For other uses, see Alarm (disambiguation). ...
A streetlight in front of a red sky at night A street light, also known as a light standard, is a raised light on the edge of a road, turned on or lit at a certain time every night. ...
They are also used in some dynamic compressors together with a small incandescent lamp or light emitting diode to control gain reduction.
Lead sulphide- and indium antimonide-LDR are used for the mid infrared spectral region. At the other end of the scale, Ge:Cu photoconductors are among the best far-infrared detectors available, and are used for infrared astronomy and infrared spectroscopy. Lead sulfide (also spelled sulphide, see Sulfur#Spelling) is a chemical compound PbS, most often purified from the mineral galena. ...
Indium antimonide (InSb) is a narrow gap semiconductor material from the group the (III-V group) used in infrared detectors, including thermal imaging cameras, FLIR systems, infrared homing missile guidance systems, and in infrared astronomy. ...
General Name, Symbol, Number germanium, Ge, 32 Chemical series metalloids Group, Period, Block 14, 4, p Appearance grayish white Standard atomic weight 72. ...
Copper has played a significant part in the history of mankind, which has used the easily accessible uncompounded metal for nearly 10,000 years. ...
For other uses, see Infrared (disambiguation). ...
Infrared astronomy is the branch of astronomy and astrophysics which deals with objects visible in infrared (IR) radiation. ...
Infrared spectroscopy (IR spectroscopy) is the subset of spectroscopy that deals with the infrared region of the electromagnetic spectrum. ...
Circuit symbol Below is a symbol for a photoresistor as used in some circuit diagrams.
 Image File history File links Light-dependent_resistor_schematic_symbol. ...
See also Optoelectronics is the study and application of electronic devices that interact with light, and thus is usually considered a sub-field of photonics. ...
The fact that traditional transistors (these days called “Bipolar Junction Transistors†or BJTs) are photosensitive has been known ever since they were invented. ...
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