　 With the successful development of 100 lm / W white LEDs , white LEDs have taken a step forward in the popularization of display and lighting applications. It mainly introduces the new application of white LED - the structure and principle of the card light, and its application in life. The brightness of the BM27 was tested at a distance of 50 mm at a current of 20 A. The average brightness was greater than 3 400 cd / m 2 and the uniformity was over 85%.
LED is an abbreviation for light emitting diode, an electric light source made of semiconductor technology. The core of the LED is a wafer consisting of a P-type semiconductor and an N-type semiconductor. There is a transition layer between the P-type semiconductor and the N-type semiconductor, called a P2N junction. In the forward conduction, the majority carriers and the minority carriers in the semiconductor recombine, and the released energy is emitted as photons or partially in the form of photons, and a large number of photons form a photon stream, that is, luminescence. When the reverse voltage is applied to the P2N junction, minority carriers are difficult to inject, so they do not emit light. Due to the different bandgap energies of semiconductor materials, LEDs of different semiconductor materials can emit light of different colors.
LED light source has the characteristics of small size, long life, low power consumption, fast reflection speed, rich color and flat package. It is an environmentally friendly and energy-saving cold light source. LEDs are widely used in display and lighting because of their above characteristics.
In 1965, the first commercial LED (red light) was introduced with an efficiency of only 0.1 lm /W. In 1968, LEDs made from GaAsP materials have reached 1 lm / W efficiency and emit red, orange and yellow light. In the early 1990s, the development of two new materials, GaAlInP with red and yellow light and Ga InN with green and blue light, led to a significant improvement in the efficacy of LEDs. In 1998, the successful development of white LEDs marked the arrival of the lighting technology revolution.
1. The latest development of white LED
When in December 2006, Japan's Nichia Chemical Industries posted a forward current of 20 mA, the luminous efficiency reach 150 lm / W white LED, the luminous efficiency of about 1.7 times that of the fluorescent improve color rendering for incandescent The lamp is 11. 5 times, even exceeding the high pressure sodium lamp which is generally considered to have the highest luminous efficiency. The Showa Denko Group (SDK) has developed a new process for the manufacture of gallium nitride (GaN) based and other nitride based high quality composite semiconductors, primarily for blue and white LEDs. In February 2007, Philip s Lumileds announced the LED epitaxial technology (which basically solves the problem that the white light high-power LED light effect decreases with current climbing, which can increase the light efficiency with the increase of the drive current. Cyberlux claims to use plastic material. The white LED is cheaper, this technology can significantly reduce manufacturing costs, and the brightness is better than traditional white LED. In March 2007, Seoul Semiconductor (SSC) launched 35,000 hours, luminous flux 96 lm of eight The angled 2 W single-chip Acriche can be plugged directly into a 110 V or 220 V AC power supply without the need for an AC/DC converter. The SSC plans to increase the Ariche efficacy to 120 lm /W by 2008.
At present, the thickness of the LED chip is only 0.4 mm, and the light extraction technology of the LED is also greatly improved. Therefore, backlights with LEDs are gradually being used in small displays such as third-generation mobile phones, PDAs, portable DVDs, and digital video cameras. In addition, various lights on the car, such as front and rear lights, side lights, headlights, interior lights and dashboard displays, will fully enter the development application. According to the statistics of Strategies Un2limited, Japan's large-scale headlight factory, Kohido, estimates that by 2008 all new cars will use LEDs as lights.
2 white LED card light
A domestic optoelectronic device Co., Ltd. is a new white LED product for Japan, named "Card Light". The product is shown in Figure 1. This is a new application of white LED and has been patented.
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