After Edison invented the carbon incandescent lamp in , lighting technology entered a new era. Reviewing the lighting history of the twentieth Century, people found out many new light sources, such as fluorescent lamps, mercury lamps, high / low pressure sodium lamps, metal halide lamps, compact fluorescent lamps, high frequency electrodeless fluorescent lamps, microwave sulfur lamps and so on. Defects of the incandescent lamp are that the bulb is fragile, it is easy to get an electric shock and power consumption of the tungsten wire is high under the condition of heating. Although fluorescent lamps save more energy than incandescent lamps, but it is not good for human vision and the mercury in the lamp tube is harmful to human body and environment. LED causes qualitative changes of lighting technology. Compared with the traditional lighting technology, LED is a semiconductor, which can convert electrical energy into visible light. LED belongs to the solid cold light source. The volume of LED is small, its weight is light and the structure is also very solid. Because of low working voltage, service life of LED is long. In accordance with the definition of light effect, LED luminous efficiency is not high, but because almost all of the LED spectra concentrate in the visible light spectrum, the efficiency can reach %~%. However, visible efficiency of incandescent lamp of the same light effect is only %~%. Generally, the power of the monomer LED is 0.~1W and LED can meet different needs through the cluster mode.
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