Light emitting Diode

Light emitting Diode

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  3 A light emittingdiode (LED) is essentially a PN junction -semiconductor that emits a monochromatic (single color) light when operated in a forward biased direction. LEDs convert electrical energy into light energy. They are frequently used as "pilot" lights in electronic appliances to indicate whether the circuit is closed or not.
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  4 The most importantpart of a light emitting diode (LED) is the semi-conductor chip located in the center of the bulb as shown at the right. The chip has two regions separated by a junction. The p region is dominated by positive electric charges, and the n region is dominated by negative electric charges. The junction acts as a barrier to the flow of electrons between the p and the n regions. Only when sufficient voltage is applied to the semi-conductor chip, can the current flow, and the electrons cross the junction into the p region.
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  5 When sufficient voltageis applied to the chip across the leads of the LED, electrons can move easily in only one direction across the junction between the p and n regions. In the p region there are many more positive than negative charges. When a voltage is applied and the current starts to flow, electrons in the n region have sufficient energy to move across the junction into the p region.
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  6 Each time anelectron recombines with a positive charge, electric potential energy is converted into electromagnetic energy. For each recombination of a negative and a positive charge, a quantum of electromagnetic energy is emitted in the form of a photon of light with a frequency characteristic of the semi-conductor material (usually a combination of the chemical elements gallium, arsenic and phosphorus)..
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  7 • Sensor Applications •Mobile Applications • Sign Applications • Automative Uses • LED Signals • Illuminations • Indicators
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  Medical Instrumentation Bar CodeReaders Color & Money Sensors Encoders Optical Switches Fiber Optic Communication 8
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  Mobile Phone PDA's Digital Cameras LapTops General Backlighting 9
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  Full Color Video MonochromeMessage Boards Traffic/VMS Transportation - Passenger Information 10
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  Traffic Rail Tower Lights Runway Lights Emergency/PoliceVehicle Lighting 11
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  12 LEDs are availablein red, orange, amber, yellow, green, blue and white. Blue and white LEDs are much more expensive than the other colours. The colour of an LED is determined by the semiconductor material, not by the colouring of the 'package' (the plastic body). LEDs of all colours are available in uncoloured packages which may be diffused (milky) or clear (often described as 'water clear'). The coloured packages are also available as diffused (the standard type) or transparent. LEDs are made from gallium-based crystals that contain one or more additional materials such as phosphorous to produce a distinct color.
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  13 Tri-colour LEDs The mostpopular type of tri-colour LED has a red and a green LED combined in one package with three leads. They are called tri- colour because mixed red and green light appears to be yellow and this is produced when both the red and green LEDs are on. The diagram shows the construction of a tri - colour LED. Note the different lengths of the three leads. The centre lead (k) is the common cathode for both LEDs, the outer leads (a1 and a2) are the anodes to the LEDs allowing each one to be lit separately, or both together to give the third colour.
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  14 Bi-colour LEDs A bi-colourLED has two LEDs wired in 'inverse parallel' (one forwards, one backwards) combined in one package with two leads. Only one of the LEDs can be lit at one time and they are less useful than the tri- colour LEDs described above.
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  Bargraph 7-segment StarburstDot matrix 15 Some Types of LEDs
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   http://www.marktechopto.com/  http://acept.la.asu.edu/courses/phs110/expmts/exp13a.html http://www.kpsec.freeuk.com/components/led.htm  http://www.fiber-optics.info/articles/LEDs.htm  http://www.theledlight.com/technical1.html  http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/leds.html  www.kpsec.freeuk.com/components/led.htm 16
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