The development process of LED history
At the very beginning, LEDs were mainly used for indicating light sources of instruments and meters, and then LEDs of various light colors appeared in traffic lights and large-area display screens and were widely used, which produced a good effect for the whole society. economic and social benefits.
Let's take a 12-inch red traffic light as an example. In the United States, a long-life, low-efficiency 140-watt incandescent lamp was used as the light source, which can produce 2,000 lumens of white light. After the red filter, the light loss rate reaches 90%, so only 200 lumens of red light is left for us to use. In the design of the new product, Lumileds used 18 red LED light sources with a total of 14 watts of electricity to produce the same light effect.
For ordinary lighting, people are more in need of white light sources. In 1998, the white light LED was successfully developed. The LED is made by encapsulating a GaN chip with yttrium aluminum garnet (YAG). The GaN chip emits blue light (λp=465nm, Wd=30nm), and the Ce3+-containing YAG phosphor made by high temperature sintering emits yellow light with a peak value of 550nm after being excited by this blue light. The blue LED substrate is mounted in a bowl-shaped reflective cavity, covered with a thin layer of resin mixed with YAG, about 200-500 nm. Now, for InGaN/YAG white LEDs, by changing the chemical composition of the YAG phosphor and adjusting the thickness of the phosphor layer, various colors of white light with a color temperature of 3500-10000K can be obtained. This method of obtaining white light through blue LED has simple structure, low cost and high technical maturity, so it is the most widely used.
