When electrons recombine with holes, they can emit visible light, so they can be used to make light-emitting diodes. Used as an indicator light in circuits and instruments, or as a text or digital display. Gallium arsenide diodes emit red light, gallium phosphide diodes emit green light, silicon carbide diodes emit yellow light and gallium nitride diodes emit blue light. Because of its chemical properties, it can be divided into organic light-emitting diode and inorganic light-emitting diode LED.
Application example of LED technology:
LED display screen: Since the mid-1980s, monochrome and multicolor display screens have appeared, initially text screens or animation screens. In the early 1990s, with the development of computer technology and integrated circuit technology, the video technology of LED display screen was realized, and TV images were directly placed on the screen. Especially in the mid-1990s, blue-green ultra-high brightness led was successfully developed and put into production, which greatly expanded the application of outdoor screens. The area varies from 100 meters to 300 meters. At present, LED display screen has been widely used in stadiums, squares, meeting places and even streets and shopping malls. The full-color screen of NASDAQ in Times Square in the United States is the most famous, with an area of 120ft× 90ft, which is equivalent to100-300m, from1900000. It is also widely used in securities quotation screen, bank exchange rate screen, interest rate screen and so on. Recently, great progress has been made in the information screen of expressways and elevated roads. The application of light-emitting diodes in this field has reached a scale, forming a new industry, and a relatively stable growth can be expected [1]? .
Traffic lights: Navigation lights have used LED as light source for many years, and the current work is to improve and perfect. Road traffic lights have made great progress in recent years, with rapid development of technology and application. At present, China has about 40,000 sets of orders every year, while California has replaced 50,000 sets of traditional light sources with LED traffic lights in recent years. From the use effect, the effect of long life, power saving and maintenance-free is obvious. At present, the peak wavelengths of LED are red 630nm, yellow 590nm and green 505nm. The problem that should be paid attention to is that the driving current should not be too large, otherwise the high temperature in the summer sun will affect the life of LED? .
Recently, LED airport-specific signal lights, which have been used as navigation lights, floodlights and omni-directional lights in airports, have also been successfully put into use, and have achieved good results in many aspects. With independent intellectual property rights, it has obtained two patents, which are reliable, energy-saving and maintenance-free, and can be popularized and applied to various airports to replace the old signal lights that have been used for decades. It is not only high in brightness, but also easy to identify signals because of the high purity of LED light color. Because there are many kinds of railway signal lamps, which need different light intensities and perspectives, they are currently being developed, and it is estimated that they will be gradually developed and put into use. In terms of quantity, it is also a considerable market? .
Ultra-bright LED for automobile lamps can be made into automobile brake lights, taillights and direction lights, and can also be used for instrument lighting and indoor lighting. It has obvious advantages over incandescent lamps in vibration resistance, power saving and long service life. When used as a brake light, its response time is 60ns, which is much shorter than that of incandescent lamp 140 ms, and the safety distance will be increased by 4-6 m when driving on a typical expressway.
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LCD backlight LED: As the backlight of LCD, it can not only be green, red, blue and white, but also be color-changing backlight. Many products have entered the stage of production and application. Recently, the LCD screens on mobile phones are all backlit by LED, which has improved the product grade and achieved good results. Using 15in (65438) composed of 8 blue, 24 green and 32 red LEDs.
Lm, brightness 18000nits (Nite, cd/m2).22 LCD backlight is also made, only 6mm thick, which not only has good color mixing effect, but also has a color rendering index above 80. Although the big backlight is in the development stage, it has great potential? .
Lighting: Due to the improvement of LED brightness and the reduction of price, plus long life and power saving, it is easier to drive and control than neon lights, and it can not only flash, but also change color. Therefore, the monochromatic, multicolor and even color-changing luminous columns made of ultra-high brightness light-emitting diodes, together with various other light-emitting units, decorate landscape projects such as tall buildings, bridges, streets and squares, showing colorful, starry and colorful scenes. Many units have LED beams. .
As the lighting source, the LED light source should be white light. See Table 3 for the classification of white LED light sources. At present, as military white LED lighting, some varieties have been put into mass production. Because LED light source has no infrared radiation, it is easy to hide, and it also has the advantages of vibration resistance, battery power supply, solid structure and portability. Special light sources will have great development. Lawn lamps and buried lamps used for folk use have been produced on a large scale, and they are also used as microscope field lighting, flashlights, surgeon headlights, museum or exhibition lighting and reading desk lamps. With the increase of luminous flux and the decrease of price, the application will be gradually expanded, and the transition from special lighting to general lighting will be completed. It is estimated that they will enter the field of general lighting in 2005-20 10.