Use introductionedit
relationship
It is well known that the wavelength range of the visible light spectrum is 380nm～760nm, which is the seven colors of light that can be felt by the human eye-red, orange, yellow, green, cyan, blue, and purple, but the seven colors of light are each A monochromatic light.
For example, the peak wavelength of the red light emitted by the LED is 565 nm. There is no white light in the spectrum of visible light, because white light is not monochromatic light, but a composite light composed of a variety of monochromatic lights, just as sunlight is white light synthesized by seven monochromatic lights, while in color TVs White light is also synthesized from the three primary colors red, green and blue.
It can be seen that, to make the LED emit white light, its spectral characteristics should include the entire visible spectral range. However, it is impossible to manufacture LEDs with this performance under process conditions. According to people's research on visible light, the white light that human eyes can see requires a mixture of at least two kinds of light, that is, two-wavelength emission (blue light + yellow light) or three-wavelength emission (blue light + green light + red light) mode . Both of the above two modes of white light require blue light, so the ingestion of blue light has become the key technology for white light manufacturing, that is, the "blue light technology" pursued by major LED manufacturing companies. There are only a few manufacturers that master the "blue light technology" in the world, so the promotion and application of white light LEDs, especially the promotion of high-brightness white light LEDs in my country, is still a process.
light source
For general lighting, in terms of process structure, white light LEDs are usually formed by two methods. The first is to use "blue technology" with phosphors to form white light; the second is to mix multiple monochromatic lights. Both of these methods have successfully produced white light devices. The first method to generate white light is shown in Figure 1. The LED GaM chip emits blue light (λp=465nm) in the picture, which is packaged with YAG (yttrium aluminum garnet) phosphor, and emits when the phosphor is excited by blue light. Yellow light, as a result, blue light and yellow light are mixed to form white light (the structure of the LED is shown in Figure 2). The second method uses chips of different colors to be packaged together, and white light is generated by mixing the colors of light.
prospect
In order to illustrate the characteristics of white LEDs, first look at the condition of the lighting source used. Incandescent lamps and halogen tungsten lamps have an optical efficiency of 12-24 lumens/watt; fluorescent lamps and HID lamps have an optical efficiency of 50-120 lumens/watt. For white LEDs: In 1998, the luminous efficiency of white LEDs was only 5 lumens/watt. By 1999, it had reached 15 lumens/watt. This index was similar to ordinary household incandescent lamps. In 2000, the luminous efficiency of white LEDs It has reached 25 lumens/watt, which is similar to the tungsten halogen lamp. Some companies predict that by 2005, the luminous efficiency of LEDs can reach 50 lumens/watt, and by 2015, the luminous efficiency of LEDs is expected to reach 150-200 lumens/watt. At that time, the working current of the white LED could reach the ampere level. This shows that the development of white light LED writers' lighting source will become a possible reality.
Although incandescent lamps and halogen tungsten lamps for general lighting are cheap, they have low luminous efficiency (the thermal effect of the lamp consumes nothing power), short life span, and heavy maintenance workload. However, if white light LEDs are used for lighting, not only high luminous efficiency, but also longevity Long (more than 10,000 hours of continuous working time), almost no maintenance.
LED light source has the advantages of low-voltage power supply, low energy consumption, strong applicability, high stability, short response time, no pollution to the environment, multi-color light, etc. Although the price is more expensive than existing lighting equipment, it is still considered to be It is inevitable to replace existing lighting devices.
