In the 1960s, scientific and technological workers developed LED light-emitting diodes using the principle of semiconductor PN junction light-emitting. The LED developed at that time was made of GaASP, and its color was red. After nearly 30 years of development, the well-known LED can emit red, orange, yellow, green, blue and other colors. However, white LEDs for lighting were developed only after 2000. Here, the readers are introduced to white LEDs for lighting.
The earliest LED light source made of semiconductor P-N junction light-emitting principle came out in the early 1960s. The material used at that time is GaAsP, which emits red light (λp=650nm). When the driving current is 20 mA, the luminous flux is only a few thousandths of lumens, and the corresponding luminous efficacy is about 0.1 lumen/watt.
In the mid-1970s, the elements In and N were introduced to make LEDs produce green light (λp=555nm), yellow light (λp=590nm) and orange light (λp=610nm), and the luminous efficacy was also increased to 1 lumen/watt.
In the early 1980s, LED light sources of GaAlAs appeared, making the luminous efficacy of red LEDs reach 10 lumens/watt.
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 luminous efficacy of LEDs.
In 2000, the luminous efficacy of the LEDs made by the former reached 100 lumens per watt in the red and orange regions (λp=615nm), while the luminous efficacy of the LEDs made by the latter in the green region (λp=530nm) could reach 50 lumens. /watt.
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