In 1993, the Japanese chemical company made a breakthrough in blue GaN LED technology and quickly industrialized. In 1996, it realized white leds and applied for multiple patent protection.
Significance: the use of a wide range, especially as a new light source -- the fourth generation of lighting source, will produce a great energy saving effect in the future.
Variegated white LED and light source has many advantages: solid, small volume, long service life (hours), seismic, not easy damaged, launch a fast response time (ns) small power consumption, pollution-free (mercury-free), etc. Governments and companies have given great enthusiasm and attention to this because of the huge lighting market and the prospect of significant energy efficiency. To this end, the United States, Japan and Europe have poured in a lot of manpower and resources to create specialized agencies and programmes to promote white-light lED research and development. In July 2001, the first U.S. proposal for a "new generation of lighting initiative" (NGLl) to provide the fund's legislative bill was submitted to congress for consideration as part of the senate energy bill S1766, Sec. 1213. The Japanese government also has a "21st century compound semiconductor". The world's leading lighting companies and semiconductor materials companies have teamed up to restructure the group to develop white ieds.
Implementation of white LED principle and scheme
There are three basic principles for white LED:
(1) blue LED chips and yellowing phosphors can be effectively excited by blue light to form white leds. Some of the blue light is absorbed by the phosphor powder, and the phosphor is stimulated to emit yellow light. The yellow light emitted is mixed with the remaining blue light, and the intensity ratio can be controlled by the white light of various colors.
(2) make a pixel of red, green and blue leds into a pixel or white light;
(3) like three base color energy-saving lamps, the ultraviolet LED chip and the uv light can be effectively excited by uv light emitting red, green, and blue fluorescent body organic combinations of white leds.
The selection of the British light body can be an efficient inorganic or organic fluorescent body or a combination of the two. Current is from blue InGaN LED chip and can be blue effectively inspire the yellow light of cerium rare earth phosphors garnet organic combination of implementation hair white LED, this is the dominant scheme, both at home and abroad have been industrialization. FIG. 3 shows the emission spectra of the typical white-light LED, which is composed of the blue-ray spectrum of the InGaN chip and the YAG: the fluorescence spectrum of the Ce system.
3.White LED light and photoelectric
From analysis of theory and technology development, white LED light efficiency can reach above 2001 m/w, white LED light 6 times within five years, the diagrams show the white light LEO from photosynthetic efficiency increase and prospective development in 1998-2002.
White leds are currently classified as two stage targets in 2005 and 2010. Since 2005, they have replaced incandescent lamps and entered commercial lighting. Enter home lighting in 2010. Two problems must be overcome to reach the intended white leds.
The cost price must be reduced to US $0.01 / lm
Light and light must be improved.
The answer is yes. People are making improvements to blue, ultraviolet LED chips, LED packaging (including fluorescent powder coating process) and fluorescent powder. For chips:
(1) development of large-size chips, such as the recently launched 900900um large-size chip of Cree corp.
(2) the manufacturing of high-power chips and chips for 5W have been brought to market, which is significantly ahead of the planned 2000 strategy seminar.
(3) the chip inversion new technology makes the external quantum efficiency improve.
(4) actively develop ultraviolet LED with shorter wavelength, so that it is much more efficient than the current YAG: Ce fluorescent powder, which is much more efficient than the three base color phosphors, so that the white leds reach the new level. A recent four-dollar AlInGaN multi-layer quantum well (MQW) technology at the university of southern California has developed an ultraviolet LED that can range from 305nm to 340nm. This is the shortest UVLED. Figure 3 shows the structure of this UVLED chip. For the 20 mu m * 1000 mu m, the emission peak is as high as 1mw at 340nm.
If the first goal is achieved, the incandescent light bulb will be replaced from 2005 to 2007, saving 10 gigawatts of power for the United States. The second goal is to enter the family lighting. In 2010-2015, the light effect of white leds reaches 150-200lm/w, and the United States can save about 25GW of electricity. Of course, we must see that there are considerable difficulties in achieving the universal illumination of 1001m/w. In the face of rare opportunities, the government actively supports the inclusion of new green lighting and energy conservation planning. But it also faces considerable challenges and intellectual property barriers. So far, efficient blue and blue-violet LED chips have not yet industrialized scale production, but China's rare earth fluorescent powder has its advantages.
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