Led Lighting Development And Lifespan

LED Called as light emitting diode,it's basic structure is a piece of electroluminescent semiconductor material, which is a solid-state semiconductor device and it can directly convert electricity into light; the heart of LED is a semiconductor Chip,The semiconductor chip consists of two parts, one is a P-type semiconductor, and the other end is an N-type semiconductor; when these two semiconductors are connected, a PN junction is formed between them; when the current acts on the chip through the wires, the electrons Will be pushed to P area,In the P zone,electrons recombine with holes, and then they emit energy in the form of photons. This is the principle of LED light emitting. The wavelength of light is also the color of light, which is determined by the material forming the P-N junction. 

1) Initial stage: White LEDs are made by encapsulating GaN chips and Yttrium Aluminum Garnet (YAG) together.

A) The GaN chip emits blue light (λp=465nm, Wd=30nm), and the Ce3+-containing YAG phosphor made by high-temperature sintering is excited by this blue light and emits yellow light with a peak of 550nm.

B) The blue LED substrate is installed in a bowl-shaped reflective cavity, covered with a thin layer of resin mixed with YAG, about 200-500nm.

C) For InGaN/YAG white LEDs, by changing the chemical composition of the YAG phosphor and adjusting the thickness of the phosphor layer, white light of various colors with a color temperature of 3500-10000K can be obtained. 

2) In the mid-1970s, the elements In and N were introduced to make the LED produce green light (λp=555nm), yellow light (λp=590nm) and orange light (λp=610nm), and the luminous efficiency was increased to 1 lumens/watt.

3) In the early 1980s, GaAlAs LED light sources appeared, making the light efficiency of red LEDs reach 10 lumens/watt.

4) In the early 1990s, two new materials, GaAlInP, which emits red and yellow light, and GaInN, which emits green and blue light, were successfully developed, which greatly improved the light efficiency of LEDs.

5) In 2000, the LED made by the former had a luminous efficiency of 100 lumens per watt in the red and orange zone (λp=615nm), while the LED made by the latter had a luminous efficiency of 50 lumens in the green zone (λp=530nm). /watt.

6) LED service life is more than 50,000 hours.