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How it started
A light-emitting diode (LED) is an electronic light source. The LED was first invented in Russia in the 1920s, and introduced in America as a practical electronic component in 1962. Oleg Vladimirovich Losev was a radio technician who noticed that diodes used in radio receivers emitted light when current was passed through them. In 1927, he published details in a Russian journal of the first ever LED.
How Leds work
LEDs differ from traditional light sources in the way they produce light. In an incandescent lamp, a tungsten filament is heated by electric current until it glows or emits light. In a fluorescent lamp, an electric arc excites mercury atoms, which emit ultraviolet (UV) radiation. After striking the phosphor coating on the inside of glass tubes, the UV radiation is converted and emitted as visible light.
An LED, in contrast, is a semiconductor diode. It consists of a chip of semiconducting material treated to create a structure called a p-n (positive-negative) junction. When connected to a power source, current flows from the p-side or anode to the n-side, or cathode, but not in the reverse direction. Charge-carriers (electrons and electron holes) flow into the junction from electrodes. When an electron meets a hole, it falls into a lower energy level, and releases energy in the form of a photon (light).
The specific wavelength or color emitted by the LED depends on the materials used to make the diode.
Red LEDs are based on aluminum gallium arsenide (AlGaAs). Blue LEDs are made from indium gallium nitride (InGaN) and green from aluminum gallium phosphide (AlGaP). "White" light is created by combining the light from red, green, and blue (RGB) LEDs or by coating a blue LED with yellow phosphor. See "
Applications
Due to the nature of all the features and benefits of LEDs they are suitable for use in a wide range of lighting applications.
Decorative Lighting
Due to the rich variety in colours, compact size, durability, energy savings, and long life LED lighting is a perfect light source for decorative application. Mounted on a PCB, flexible PCB, cable wire, or other electrically conductive materials LEDs are versatile and are being applied to the entire range of decorative lighting.
General and Commercial Illumination
With the advance of the WLED (White LED) technology applied singularly, in clusters, or arrays are now bright enough to be used for general and commercial illumination. Homes, offices, public buildings, shopping centres and the like all around the world are applying new WLED based illumination products.
LCD Backlight
Because of LEDs compact size, durability, energy savings, long life, and low power consumption, LEDs are perfect light sources for various backlight displays.
Display
Indoor and outdoor visual display systems are rapidly becoming the mainstay of the display and signage industry. The affordability of LED based screens and displays are also rapidly becoming more cost effective through a variety of designs, resolutions and varied pixel pitch. The largest LED display in the world is 36m high located in Times Square, Manhattan, USA.
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