60's of last century, scientists used the principle of light-emitting semiconductor PN junction, the development became light-emitting diode LED. Was developed by the LED, the materials used are GaASP, its light color is red. After nearly 30 years of development, it is now very familiar with the LED, has been able to send red, orange, yellow, green, blue and other shade. However, the white light LED lighting is only required only in recent years to develop, here to introduce the reader to the lighting with white LED.
1. LED white light visible light spectrum and the relationship. All the week, the wavelength range of visible light spectrum 380nm ~ 760nm, the human eye can feel the seven colors of light - red, orange, yellow, green, green, blue, purple, but each of the seven colors of light are a A monochromatic light. For example, the red LED made peak wavelength of 565nm. In the visible spectrum of light is not white, because white light is not monochromatic, but the compound synthesized by a variety of monochromatic light, monochromatic light as the sun light is the synthesis of seven white light, and color TV in white by the three primary colors of light are red, green, blue synthesis. Thus, to make white light LED, which should include the entire visible spectral characteristics of the spectrum. But to create this performance LED, under the present conditions is impossible. According to one study of visible light, human eyes can see is white, mixed at least two kinds of light, ie light wavelength (blue light + yellow light) or three-wavelength light (blue light + green light + red light) mode . These two modes of white light, blue light are required, so the intake of white light blue light has become a key manufacturing technology, the current major LED manufacturer chasing the "Blu-ray technology." Current international control "Blu-ray technology" only a few vendors, such as Japan's Nichia, Toyoda Gosei of Japan, the United States CREE, Osram of Germany and so on, so the promotion of white LED applications, particularly high-brightness the promotion of white LED in China there is a process.
2. White LED technology structure and white light. For general lighting, in the process structure, the white LED is usually formed in two ways, first is the use of "Blu-ray technology" and with the formation of white phosphor; second hybrid approach is a variety of monochromatic light. Both methods have been successfully produce white light devices. The first method to produce white light system shown in Figure 1, the figure LEDGaM blue chip fat (λp = 465nm), it YAG (yttrium aluminum garnet) phosphor package together, when the phosphor excited by blue light yellow light, results, blue and yellow mixed to form white light (LED structure form shown in Figure 2). The second method uses different shade of the chip package together, a mixture of colored light produced by white light.
3. White LED lighting, new light source applications. To illustrate the characteristics of white LED, the first look at the current light source used for lighting conditions. Incandescent and halogen, the optical efficiency of 12 ~ 24 lm / W; fluorescent and HID lamps light efficiency of 50 ~ 120 lumens / watt. The white LED: In 1998, white LED light effect only 5 lm / W, by 1999 had reached 15 lm / W, this indicator is similar to ordinary household incandescent light, and in 2000, the white LED light effect than 25 lm / W, similar to the indicators and halogen. There predicts that by 2005, LED light efficiency up to 50 lm / W, 2015, LED light efficiency is expected to reach 150 ~ 200 lumens / watt. At that time the white LED current can Daan Pei-level work. This shows that development of white LED light source with writers, will become a possible reality.
Ordinary incandescent and halogen lighting, although cheap, but the light efficiency is low (in vain thermal effect of light power), short life, maintenance workload, but if the use of white LED for illumination, not only the high luminous efficiency, and life long (more than 10,000 hours continuous working time), almost no maintenance. Currently, the German company Hella has developed the aircraft using white LED reading lights; a street in the Australian capital Canberra have been used for a white LED street lighting; China's urban traffic control lights are being replaced with white LED lights early in the traffic order. Can be expected in the near future, the white LED will enter the home to replace the existing lighting.
LED light source with the use of low power, low energy consumption, applicability, high stability, short response time, environmental pollution, such as the advantages of multi-color light, while prices expensive than the existing lighting equipment, it is still considered Inevitably, existing lighting devices.
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