Fifty years ago, people have known about the basic knowledge of the semiconductor materials that can produce the ray o light. LED is the abbreviation of light emitting diode; its basic structure is a piece of electroluminescent semiconductor materials. It is fixed on a shelf with the lead and sealed around with epoxy resin, namely the solid encapsulation, which can protect the internal core line. Therefore, LED has very good earthquake resistant performance.
At the beginning, LED is used for the pointing light source of the instrument and meter. Later, LED with various colors has been widely applied in traffic lights and display screen in large areas, which has a good economic benefits and social effects. Take the red traffic lights for example, in USA, 140 watt filament lamp of long life and low light efficiency is used as the light source, it can produce the white light of 2000 lumens. Through the red optical filter, the light loss is 90%; there is only red light of 200 lumens left.
Principle of LED Chips
LED（Light Emitting Diode）is a kind of solid semiconductor device, which can directly transform the electricity to the light. The heart of LED is a semiconductor chip. One end of the chip is attached on a holder, one end is the negative polar, and the other end is the positive end connecting to the power supply, which makes the whole chip encapsulated in the epoxy resin. The semiconductor chip is composed of two parts, one part is P type semiconductor, the electron hole plays a dominant role, the other end is N type semiconductor, and there are many electrons. When these two kinds of semiconductor are connected to each other, they will form a P-N junction among themselves. When the current plays role in this chip through guide line, the electrons will be pushed to P zone, the electrons will compound the holes in P zone, and then it will produce the energy in the form of photon. This is LED illuminating principle. However, the wavelength of light is also the color of Light; this is determined by P-N junction materials.
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