Overview of the development history and application trends of LED display devices[汽车修理知识]

New LEDmonitorComponents have the advantages of low power consumption, high brightness, long life, and small size. This article starts from the brief history of the development of LED display devices and discusses surface mount LEDs,carThe development trend of applied LEDs and lighting LEDs has certain reference value for Chinese engineers engaged in the development of display devices.
The world's first commercialized light-emitting diode (LED) was made of germanium in 1965, and its unit price was US$45. Soon afterwards, Monsanto and Hewlett-Packard also launched commercial LEDs made of GaAsP materials. These early red LEDs can provide an output luminous flux of about 0.1 lumens per watt, which is 100 times lower than the 15 lumens of a typical 60 to 100 watt incandescent lamp.
In 1968, breakthroughs were made in the research and development of LEDs. The efficiency of GaAsP devices reached 1 lumen/watt by using the nitrogen doping process, and they were able to emit red, orange and yellow light. By 1971, the industry introduced GaP green bare chip LEDs with the same efficiency.
Since 1972, a small number of LED displays have been used in clocks and calculators. The world's first LED-enabled watch was originally sold in expensive jewelry stores, and its price was as high as US$2,100. Almost at the same time, HP and Texas Instruments also introduced calculators with 7-segment red LED displays.
By the 1970s, due to the large number of applications of LED devices in home and office equipment, the price of LEDs plummeted. In fact, LED was the dominant digital and text display technology of that era. However, in many commercial devices, LED displays have 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 for background patterns, and bar graph arrays. The size and complexity of digital display screens continue to grow, from 2 digits to 3 digits or even 4 digits, from 7-segment numbers to 14 or 16-segment arrays capable of displaying complex combinations of text and patterns. By 1980, manufacturers began to provide intelligent dot matrix LED displays.
A major technological breakthrough in the early 1980s was the development of AlGaAs LEDs, which can emit red light with a luminous efficiency of 10 lumens per watt. This technological advancement allows LEDs to be used for outdoor sports information release and high-mounted stop lights (CHMSL) equipment in the center of the car. In 1990, the industry developed AlInGaP technology that can provide the best red device performance, which is 10 times higher than the standard GaAsP device performance at the time.
Today, the brightest material should be the transparent substrate AlInGaP. From 1991 to 2001, further developments in material technology, die size and shape have increased the luminous flux of commercial LEDs by nearly 20 times.
The continuous development of high-intensity blue LEDs has produced several generations of increasingly brighter devices. The efficiency of the LED based on silicon carbide (SiC) die material introduced around 1990 is about 0.04 lumens/watt, and the emitted light intensity rarely exceeds 15 millicandels. A technological breakthrough in the mid-1990s realized the first practical LED based on GaN. Many companies are now using different substrates such as sapphire and SiC to produce GaN LEDs that can emit green, blue or violet colors. The invention of the bright blue LED makes it possible to realize the real-color advertising display screen, which can display real-color, full-motion video images.
The emergence of blue LEDs enables people to use reverse conversion phosphorescent materials to partially convert higher-energy blue light into other colors. The blue light and the yellow light of the conversion phosphor can be combined to obtain white light, and the appropriate amount of blue light and reddish orange phospher can be combined to produce a slightly peach or purple color. Now only the LED light source can completely cover all the saturated colors in the CIE chromaticity curve, and the organic integration of various color LEDs and phosphors can produce almost unlimited colors.
In terms of reliability, the half-life of an LED (that is, the time for the light output to decrease to half of the initial value) is about 10,000 to 100,000 hours. On the contrary, the half-life of a small indicator type incandescent lamp (here the half-life refers to the time when half of the lamps fail) typically ranges from 100,000 to thousands of hours, depending on the lamp's rated operating current.