2024-04-30
Monochromatic LED types and their development history
Monochromatic LED types and their development history
The first LED light source made of semiconductor P-N junction luminescence principle came out in the early 1960s. The material used at that time was GaAsP, which emits red light (λp =650nm), and when the driving current is 20 mA, the luminous flux is only a few thousandths of a lumen, and the corresponding luminous efficiency is about 0.1 lumen/watt. In the mid-1970s, the introduction of elements in and N made the LED produce green light (λp =555nm), yellow light (λp =590nm) and orange light (λp =610nm), and the light efficiency was also increased to 1 lumen/watt. By the early 1980s, GaAlAs LED light sources appeared, making the red LED light efficiency up to 10 lumens/watt. In the early 1990s, the development of two new materials, GaAlInP with red and yellow light and GaInN with green and blue light, greatly improved the luminous efficiency of LED. In 2000, the LED made of the former in the red, orange region (λp =615nm) light efficiency reached 100 lumens/watt, while the LED made of the latter in the green region (λp =530nm) light efficiency can reach 50 lumens/watt.
The application of monochromatic light LED
Initially, LED was used as an indicator light source for instrumentation, and later LED of various light colors was widely used in traffic lights and large-area displays, resulting in good economic and social benefits. The 12-inch red traffic light, for example, was originally a long-life, low-efficiency 140-watt incandescent light source in the United States, which produced 2000 lumens of white light. After passing through the red filter, the light loss is 90%, leaving only 200 lumens of red light. In the new design, Lumileds uses 18 red LED light sources, including circuit losses, a total of 14 watts of power, can produce the same light effect.
Car signal lights are also an important area of LED light source applications. In 1987, China began to install high brake lights on the car, because the LED response speed is fast (nanosecond level), you can let the driver who follows the vehicle know the driving condition as early as possible, reduce the occurrence of car rear-end accidents.
In addition, LED lights in outdoor red, green, blue full-color display, key link miniature torches and other fields have been applied.
Car signal lights are also an important area of LED light source applications. In 1987, China began to install high brake lights on the car, because the LED response speed is fast (nanosecond level), you can let the driver who follows the vehicle know the driving condition as early as possible, reduce the occurrence of car rear-end accidents.
In addition, LED lights in outdoor red, green, blue full-color display, key link miniature torches and other fields have been applied.
Development of white LED
For general lighting, people need more white light sources. In 1998, the white light LED was developed successfully. This LED is made by packaging GaN chips and yttrium aluminum garnet (YAG) together. GaN chip emits blue light (λp =465nm, Wd=30nm), and the YAG phosphor containing Ce3+ made of high temperature sintering is excited by this blue light and emits yellow light emission, with a peak value of 550nm. The blue LED substrate is installed in a bowl shaped reflection cavity and covered with a thin layer of resin mixed with YAG, about 200-500nm. Part of the blue light emitted by the LED substrate is absorbed by the phosphor, and the other part of the blue light is mixed with the yellow light emitted by the phosphor, and white light can be obtained. Now, for InGaN/YAG white leds, by changing the chemical composition of the YAG phosphor and adjusting the thickness of the phosphor layer, you can obtain a color temperature of 3500-10000K white light.
