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Principle Of LED Lights
Jun 06, 2018

LED (Light Emitting Diode), a solid semiconductor device capable of converting electrical energy into visible Light, can convert electricity into Light directly. The heart of an LED is a semiconductor wafer, one end of which is attached to a bracket and the other end is connected to the positive end of the power supply, so that the entire chip is encapsulated by epoxy resin.

A semiconductor chip consists of two parts, one is a p-type semiconductor, in which holes dominate, the other is an n-type semiconductor, and on this side are mainly electrons. But when these two semiconductors are connected, they form a p-n junction. When a current flows through a wire to the chip, the electron will be pushed P area, electron and holes in the P zone compound, then will be issued in the form of photon energy, this is the principle of LED light. The wavelength of light, the color of light, is determined by the material that forms the p-n junction.

LED can emit red, yellow, blue, green, green, green, orange, purple and white light directly. [1]

Initially LED is used as the indicator light instrument and then all kinds of light color of LED traffic light and display screen has been widely applied in large area, produced good economic and social benefits. Take a 12-inch red traffic light, for example. In the United States, a 140 watt incandescent lamp with a long life and low optical efficiency is used as a light source, producing 2,000 lumens of white light. After passing through the red filter, the light is lost 90%, leaving only 200 lumens of red light. In the new design, Lumileds USES 18 red LED lights that consume 14 watts of power, including circuit losses, to produce the same light effect. Automobile signal lamp is also an important field of LED light source application.

For general lighting, people need white light source more. LED with white light was developed successfully in 1998. The LED is made from GaN chips and yttrium aluminum garnet (YAG). GaN chip generates blue light (465nm, Wd=30nm), and the high temperature sintered YAG fluorescent powder containing Ce3+ emits yellow light when stimulated by this blue light, with a peak value of 550nLED m. The blue-ray LED substrate is installed in a bowl-shaped reflecting chamber and covered with a thin layer of resin mixed with YAG, about 200-500nm. The blue light from the LED substrate is partly absorbed by the phosphor, and the other part is mixed with the yellow light from the phosphor to get white light.

For InGaN/YAG white LED, color white light of color temperature 3500-10000k can be obtained by changing the chemical composition of YAG phosphor and adjusting the thickness of the phosphor layer. This method of obtaining white light through blue light LED is simple in construction, low in cost and high in technology maturity, so it is most used.