The earliest application of the LED light source made by the principle of semiconductor P-N junction light was introduced in the early 1960s. The material used at that time was GaAsP, which emits red light (λp = 650 nm). When the driving current is 20 mA, the luminous flux is only a few thousandths of lumens, and the corresponding optical performance is about 0.1 lm/W.
In the mid-1970s, the elements In and N were introduced to produce green light (λp=555 nm), yellow light (λp=590 nm) and orange light (λp=610 nm), and the optical performance was also improved to 1 lm/W.
By the early 1980s, the LED light source of GaAlAs appeared, making the red LED's optical performance up to 10 lumens per watt.
In the early 1990s, the development of two new materials, GaAlInP, which emits red light and yellow light, and GaInN, which emits green and blue light, have greatly improved the optical performance of LEDs.
In 2000, the former made LEDs in the red and orange regions (λp=615nm) with a luminous efficacy of 100 lumens per watt, while the latter made LEDs with a luminous efficacy of 50 lumens in the green region (λp=530nm). /watt.