How LED Solid State Lighting Works
SOLID STATE VS TRADITIONAL LIGHT SOURCESReference: US Dept of Energy
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Light Emitting Diodes – otherwise known as 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.
Solar Cells and LEDs are diodes made from semi-conductor materials. This is why they are referred to as “solid state” devices. A solar cell relies on the properties of semi-conductor materials such as silicon to convert photons into electricity. Conversely an LED may rely on indium gallium nitride to convert electricity into photons. Both devices are Direct Current (DC) as compared to Alternating Current (AC).
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An LED, in contrast, is a semiconductor diode. It consists of a chip of semi-conducting 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 "Color Quality" section for more information.
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Why Solid State (LED) Lighting?1
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LEDs can provide 50,000 hours or more of life, which can reduce maintenance costs. In comparison, an incandescent light bulb lasts approximately 1,000 hours. Fluorescents are rated for 10,000 hours under ideal conditions.
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SolarOne’s LEDs systems provide 70 lumens per watt, compared to 14-20 lumens per watt for halogen or incandescent lighting and 35 to 60 lumens per watt for compact fluorescent lighting. LEDs are especially advantageous for colored lighting applications because filters are not needed.
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LEDs have minimum ultraviolet and infrared radiation.
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LED systems are low voltage and are generally cool to the touch.
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The small size of LEDs makes them useful for lighting tight spaces
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LEDs have no filament to break and can withstand vibrations.
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Fluorescent and mercury vapor lighting contain mercury, which is hazardous to the environment and must be disposed of properly. LED’s don’t contain mercury and are not considered hazardous waste.
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LED lighting systems have already proved to be very effective in indicator applications where brightness, visibility and long-life are important, such as in exit signs and traffic signals. New uses for LEDs in the general illumination market include small-area lighting, such as parking lots and pathway and step marking. As white LEDs become more powerful and effective, LEDs will be used in more general illumination applications. |
1) From Lighting Research Center at Rensselaer Polytechnic Institute