Illumination is to provide light for humans to perceive the world with the eyes and to identify objects. The sun is the best source of light for natural and cheap, and where it is not exposed to sunlight, humans need to be illuminated with artificial light. The use of illumination sources by humans has gone through simple light sources such as candles, oil lamps and gas lamps, to incandescent lamps invented by Edison, to fluorescent lamps, halogen lamps, high-pressure sodium lamps, metal halide lamps, and trichromatic fluorescent lamps. The emergence of various electric light sources has brought more and more light to the world, and it has also brought more and more problems in energy conservation and environmental protection. In the late 1990s, the emergence of white LEDs made it possible to save energy and environmentally friendly solid-state lighting.
LED has the characteristics of high efficiency, energy saving, green environmental protection, long service life, fast response, safe and reliable, and flexible use. It has been widely recognized as the fourth generation of revolutionary illumination source after kerosene lamp, incandescent lamp and gas discharge lamp. .
In the forty years since the first LED was introduced in 1962, the LED package has undergone many evolutions. From the glass-shell package of the 1960s to the epoxy package of the 1970s, to the four-legged piranha package, the SMD package, the high-power package, and the chip-integrated COB package in the mid-to-late 1990s. With the deepening of high-power LEDs in semiconductor lighting applications, the package form has undergone many changes in just a few years.
Table 1 Comparison of main performance indicators of various illumination sources
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