LED flashlight--Introduction to the principle of LED flashlight

Atom electrons have many energy levels. When electrons transition from a high energy level to a low energy level, the energy of the electrons decreases, and the reduced energy is converted into photons and emitted. A large number of these photons is the laser. The principle of LED light emission is similar. But the difference is that the LED does not emit light through the electronic transition inside the atom, but by applying a voltage across the PN junction of the LED, so that the PN junction itself forms an energy level (in fact, a series of energy levels) level), and then electrons jump at this energy level and produce photons to emit light. New LED display devices have the advantages of low power consumption, high brightness, long life, and small size. This article begins with a brief history of the development of LED display devices, and discusses the development of surface mount LEDs, LEDs in automotive applications, and LEDs for lighting. The development trend has certain reference value for Chinese engineers engaged in the development of display devices. The world's first commercial light-emitting diode (LED) was made of germanium in 1965, and its unit price was US$45. In 1968, a breakthrough was made in the research and development of LEDs. The efficiency of GaAsP devices reached 1 lumen/watt by using nitrogen doping technology, and it was able to emit red, orange and yellow light. By 1971, the industry introduced GaP green die LEDs with the same efficiency. In 1972, a small number of LED displays were used in clocks and calculators. The world's first watch to use LEDs was originally sold in expensive jewelry stores for as much as $2,100. Almost at the same time, Hewlett-Packard and Texas Instruments introduced calculators with seven-segment red LED displays. By the 1970s, the price of LEDs plummeted due to the large number of applications 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 have also gradually received fierce competition from other display technologies, such as liquid crystal, plasma and vacuum fluorescent tube displays. This kind of competition encourages LED manufacturers to further expand their product types and actively seek applications where LEDs have obvious competitive advantages. Since then, LEDs have been used in text dot matrix displays, light grids and bar graph arrays for background patterns. Digital displays continue to grow in size and complexity, from 2 digits to 3 or even 4 digits, from 7-segment numbers to 14- or 16-segment arrays capable of displaying complex combinations of text and graphics. By 1980, manufacturers began to provide intelligent dot matrix LED displays. This technological advancement enables LEDs to be used in outdoor sports information dissemination and automotive center high mounted stop light (CHMSL) equipment. The invention of bright blue LEDs made possible the realization of true-color advertising displays capable of displaying true-color, full-motion video images. The emergence of blue LEDs enables people to partially convert higher-energy blue light into other colors by using reverse-converted phosphorescent materials. All saturated colors in the CIE chromaticity curve can be completely covered with only LED light sources, and the organic integration of various color LEDs and phosphors can produce almost any color without limitation. In terms of reliability, LEDs have a half-life (the time it takes for light output to drop to half of its original value) to be around 10,000 to 100,000 hours. In contrast, the half-life of small indicating incandescent lamps (half-life here refers to the time when half the number of lamps fail) typically ranges from 100,000 to thousands of hours, depending on the rated operating current of the lamp.