Electrons in atoms have many energy levels. When an electron jumps from a high energy level to a low energy level, the energy of the electron is reduced, and the reduced energy is converted into photons and emitted. Many of these photons are lasers. The principle of LED is similar. But the difference is that LED doesn't emit light through electronic transition inside atoms, but by applying voltage across the PN junction of LED, the PN junction itself forms an energy level (actually a series of energy levels), and then electrons jump on this energy level to produce photon emission.

The new LED display device has the advantages of low power consumption, high brightness, long life and small size. Based on the brief history of LED display devices, the development trends of surface mount LED, automotive LED and lighting LED are discussed, which has certain reference value for engineers engaged in display device development in China. 1965 The world's first commercial light-emitting diode (LED) was made of germanium, and the unit price was $45. 1968, LED research and development made a breakthrough. Through nitrogen doping process, the efficiency of GaAsP device reaches 1 lumen/watt, and it can emit red light, orange light and yellow light. As high as 197 1, the industry has introduced GaP green bare LED with the same efficiency. Since 1972, a small number of LED display screens have been used for clocks and calculators. The world's first watch with LED was originally sold in expensive jewelry stores, and the price was as high as 2 100 USD. Almost at the same time, HP and Texas Instruments also introduced calculators with seven red LED displays. In 1970s, the price of LED plummeted due to the wide application of LED devices in home and office equipment. In fact, LED was the main digital and text display technology of that era. However, in many commercial devices, LED display screens are gradually facing fierce competition from other display technologies, such as liquid crystal, plasma and vacuum cathode fluorescent lamp display. This kind of competition urges LED manufacturers to further expand product types and actively seek applications with obvious competitive advantages. Since then, light emitting diodes have been applied to text dot matrix displays, background patterns and light grids of bar graph arrays. The size and complexity of digital display screen are getting higher and higher, from 2 digits to 3 digits or even 4 digits, from 7 digits to 14 or 16 segment array that can display complex text and pattern combinations. By 1980, manufacturers began to provide intelligent dot matrix LED display screens. This technological progress enables LED to be applied to outdoor sports information release and CHMSL equipment installed in the center of the car. The invention of bright blue LED makes it possible to realize true color advertising display screen, which can display true color and full dynamic video images.

The appearance of blue LED enables people to use inverted phosphorescent materials to convert the blue light with higher energy into other colors. At present, all saturated colors in CIE chromaticity curve can be completely covered by LED light source, and the organic combination of LEDs and phosphorus of various colors can produce almost any color indefinitely. In terms of reliability, the half-life of LED (that is, the time when the light output is reduced to half) is about 1000 ~ 10000 hours. On the contrary, the typical half-life of small indicator incandescent lamps (half-life here refers to the time when half of the lamps fail) ranges from 654.38 million to several thousand hours, depending on the rated working current of the lamps. The resources come from lamps road /design_detail.asp? id=246