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  Quality creates the future,Details determine perfection
A 30-year review of the development of LED display
Source: | Author:mthinkled | Published time: 2019-01-23 | 2842 Views | Share:
A 30-year review of the development of LED display
   The earliest GaP, GaAsP, red, yellow, and green light-emitting inefficiency of the earliest GaP, GaAsP in the 1970s have begun to be applied to indicators, numbers, and text displays. Since then LED began to enter a variety of applications, including aerospace, aircraft, automotive, industrial applications, communications, consumer products, etc. , throughout the national economy and thousands of households. By 1996, LED sales worldwide had reached several billion dollars. Although LED has been limited by color and luminous efficiency for many years, gaP and GaAsP LEDs have long life, high reliability, low operating current, and compatibility with TTL, CMOS digital circuits and many other advantages, but have been the user's green. In the last ten years, high brightness and all-colorization have been the cutting-edge topics in the research of LED materials and device process technology. Ultra-high brightness (UHB) refers to LEDs with a luminous intensity of 100mcd, also known as the Candela (cd) class LED. The development of high-brightness A1GaInP and InGaN LEDs has progressed very rapidly and has reached the level of performance that is not possible with conventional materials GaA1As, GaAsP and GaP. In 1991, Toshiba Corporation of Japan and HP Corporation of the United States developed InGaA1P 620nm orange ultra-high brightness LED, in 1992 InGaA1p590nm yellow ultra-high brightness LED practical. In the same year, Toshiba developed InGaA1P 573nm ultra-high-brightness LED, with a magic light intensity of 2cd. In 1994, Japan's Niya developed inInGaN 450nm blue (green) color ultra-bright LEDs. So far, the color display required three-base red, green, blue and orange, yellow multi-color LED have reached the Kandra-level luminous intensity, to achieve ultra-high brightness, all-color, so that the light pipe outdoor all-color display become a reality. China's development LED started in the 1970s, the industry appeared in the 1980s. There are about 100 enterprises in the country, 95% of the manufacturers are engaged in the rear package production, the required core is almost all imported from abroad. Through several "five-year plan" of technical transformation, technical research, the introduction of foreign advanced equipment and some key technologies, so that China's LED production technology has taken a step forward. 
The performance of ultra-high-brightness LEDs: 
Compared with GaAsP-GaP LEDs, the luminous efficiency of the transparent-lined Low (TS) A1GaAs LED (640nm) is close to 10lm/w, which is 10 times larger than the red GaAsP-GaP LED. The ultra-bright InGaAlP LEDs are available in the same colors as GaAsP-GaP LEDs: green yellow (560nm), light green yellow (570nm), yellow (585nm), light yellow (590nm), orange (605nm), light red (625nm deep red (640nm). The luminous efficiency of transparent substrate A1GaInP LED is compared with other LED structures and incandescent light sources, the Lumen efficiency of InGaAlP LED absorption substrate (AS) is 101m/w, and the transparent substrate (TS) is 201m/w. The lumen efficiency of gaAsP-GaP LEDs is 10-20 times higher in the 590-626nm wavelength range and 2-4 times higher than that of GaAsP-GaP LEDs in the 560-570 wavelength range. Ultra-bright InGaN LEDs offer blue and green light with wavelength ranges of 450-480nm, blue green at 500nm and green at 520nm, and lumen efficiency of 3-151m/w. Ultra-high-brightness LEDs now have more lucanlum efficiency than incandescent lamps with filters, replacing incandescent lamps with a power of less than 1w, and LED arrays that can replace incandescent lamps with a power of less than 150w. For many applications, incandescent lamps are filtered to get red, orange, green, and blue, while ultra-high-brightness LEDs can get the same color. In recent years, the ultra-high-brightness LEDs made by AlGaInP materials and InGaN materials combine multiple (red, blue, green) ultra-high-brightness LED chips to get a variety of colors without filters. Including red, orange, yellow, green, blue, the current luminous efficiency has exceeded incandescent lamps, is approaching fluorescent lamps. The luminous brightness has been higher than 1000mcd, to meet the needs of outdoor all-weather, all-color display, with LED color large screen can represent the sky and the ocean, to achieve 3D animation. The new generation of red, green and blue ultra-high-brightness LEDs deliver unprecedented performance. 
Applications of ultra-high-brightness LEDs: 
1. Information LIGHT 
The automotive signal indicates that the car indicator sits mainly on the exterior of the car, mainly the directional lights, tail lights and brake lights, and the interior of the car is mainly the lighting and display of various instruments. Ultra-bright LEDs for automotive indicators have many advantages over traditional incandescent lamps and have a wide range of markets in the automotive industry. Leds can withstand strong mechanical shocks and vibrations. The average operating life MTBF is several magnitudes higher than incandescent bulbs, far higher than the car's own operating life, so LED brake lights can be packaged as a whole without regard for repair. The transparent substrateal.GaAs and AlInGaP LEDs have a fairly high lumen efficiency compared to incandescent bulbs with filters, allowing LED brake and direction lamps to operate at lower drive currents, typically only 1/4 of the incandescent bulbs, reducing the distance used by cars. Lower electrical power also reduces the volume and weight of the car's internal line system, while also reducing the internal temperature rise of integrated LED beacons, allowing lenses and covers to use less temperature-resistant plastics. LED brake lights have a response time of 100ns, which is shorter than incandescent response times, which leaves the driver with more reaction time and improves the safety of the car. The light and color of the exterior indicators of the car are clearly defined. The interior lighting of the car shows that although it is not controlled by the government as the external traffic lights, the manufacturer of the car has requirements for the color and illumination of the LEDs. GaP LEDs have long been used in in-car, and the ultra-high-brightness AlGaInP and InGaN LEDs will replace in-car incandescent lamps because they meet the manufacturer's requirements in terms of color and illumination. From the price point of view, although LED lamps and incandescent lamps are still more expensive, but from the overall system, the price of the two there is no obvious difference. With the development of ultra-high brightness TS AlGaAs and AlGaInP LEDs, prices have been falling in recent years and will be even greater in the future.

Traffic signal indicators: with ultra-high brightness LED instead of incandescent lamps, used in traffic lights, warning lights, sign lights are now all over the world, the market is vast, demand is growing rapidly. According to the U.S. Department of Transportation in 1994, there are 260,000 intersections in the United States where traffic lights are installed, and there must be at least 12 red, yellow, and blue-green lights at each intersection. Many intersections also have additional signs of transformation and pedestrian warning lights across the road. In this way, each intersection can have 20 beacons and glow at the same time. This results in about 135 million traffic lights in the United States. At present, the use of ultra-high brightness LED to replace the traditional incandescent lamp to reduce power loss has achieved significant results. Japan uses about 1 million kilowatts of electricity per year on traffic lights, and when ultra-bright LEDs replace incandescent lamps, it consumes only 12% of its electricity. 
Traffic lights Each country's competent departments should formulate the corresponding specifications, the color of the signal, the minimum lighting intensity, the map of the spatial distribution of the beam and the requirements of the installation environment. Although these requirements are written in canindescent lamps, they are generally applicable to the ultra-high-brightness LED traffic lights currents currently in use today. LED traffic lights have a longer working life compared to incandescent lamps, which can generally last up to 10 years, reducing the expected life expectancy to 5-6 years, taking into account the impact of harsh outdoor conditions. At present, ultra-high brightness AlGaInP red, orange, yellow LED has been industrialized, the price is also relatively cheap, if the red ultra-high brightness LED module to replace the traditional red incandescent traffic light head can be due to the sudden failure of red incandescent lamp to the minimum impact on safety. General LED traffic signal module consists of several sets of series LED single lights, with 12-inch red LED traffic signal module as an example, in 3-9 sets of series LED single lights, each group of series LED single light number of 70-75 (total number of 210-- 675LED single light), when there is an LED single lamp failure, only affects one set of signals, the remaining groups are reduced to 2/3 (67%) or 8/9 (89%), and will not fail the entire lamp head like an incandescent lamp. 
The main problem of the led traffic signal module is that the manufacturing is still high, with the 12-inch TS-AlGaAs red LED traffic signal module as an example, first used in 1994, its cost is 350$, and by 1996 the performance of the better 12-inch AlGaInP LED traffic signal module, the cost is 200$. It is not expected for long that the price of the InGaN blue-green LED traffic signal module will be comparable to ThatGaInP. Although the cost of incandescent traffic light head is low, but the power consumption is large, a diameter of 12 inches of incandescent traffic light head power consumption of 150W, cross the road sidewalk traffic warning lights consumption of 67W, according to calculation, each intersection of incandescent lights annual power consumption of 18133KWh, equivalent to 14 annual electricity charges 50$; however, the LED traffic signal module is very power-saving, each 8-12 inch red LED traffic signal module power consumption of 15W and 20W, the intersection corner LED signs can be used arrow switch, power consumption is only 9w, according to calculation, each intersection can save 9916KWh per year, a considerable annual savings of 793$. Based on the average cost of 200 UDper per LED traffic signal module, the red LED traffic signal module can recover the initial cost cost after 3 years with its savings in electricity, and begin to reap the economic rewards. Therefore, the current use of AlGaInP LED traffic information module, although the cost appears to be ground, but in the long run, it is still cost-effective. 
2. Big screen display 
Large-screen displays are another huge market for ultra-high-brightness LED applications, including: graphics, text, digital monochrome, two-color, and full-color displays. The various uses of LED display are listed in Table 2. Traditional large-screen active display generally uses incandescent lamps, fiber optics, cathode ray tubes, etc. Table 3 lists several displayed performance comparisons. LED display has been limited by the performance and color of the LED itself. Today, ultra-high-brightness AlGaInP, TS-AlGaAs, inGaN LEDs are available in bright red, yellow, green and blue colors to fully meet the requirements for large-screen all-color displays. LED display can be assembled by pixel size into a variety of structures, small pixel diameter is generally less than 5mm, monochrome display of each pixel with a T-1 (3/4) LED light, two-color display of each pixel for two-color T-1 (3/4) LED light, full-color display requires 3 T-1 red, green, blue lights, or an assembly of a multi-chip T-1 (3/4) pixel as an LED lamp. Large pixels are made up of many T-1 (3/4) red, green, and blue LED lights. With InGaN (480nm) blue, InGaN (515nm) green and ALGaAS (637nm) red LED light as the LED display of the three-base color, can provide realistic full-color performance, and has a large color range includes: blue and green, green and red, and the International Television Systems Commission (NTSC) set the TV color range is basically in line with. 
3. Back lighting of liquid crystal display (LCD) 
At least 10% of the liquid crystal display uses active light as back lighting, the light source can make the LCD display in a dark environment easy to read, full-color LCD display also needs a light source. The main light sources required for LCD back lighting are: incandescent bulbs, field luminescence, cold cathode fluorescence, LEDs, etc., which are listed in Table 4 for comparison, of which LEDs are the most competitive in LCD back lighting, and the new ultra-high brightness AlGaInP, AlGaAs, InGaN LEDs can provide high-efficiency luminescence and wide range of colors. 
There are three main ways for THE USE of LEDs for LCD back lighting. (1) The simplest is to install the LED lamp directly behind the LCD scattering film, can be used in many packages of LED lights, they should have a very wide beam angle, so that axial light uniformity is better. Unpackaged cores can also be used, generally using GaP LEDs, but with AlGaInP, TS-AlGaAs LEDs can operate at small currents, reducing power consumption. (2) Another way is edge light LCD back lighting, with a transparent or translucent rectangular plastic block as the light guide, it is directly placed behind the LCD scattering film, the back surface of the plastic block coated with white reflective material, LED light from one side of the plastic block, the rest of the side as a white reflective material. (3) The light emitted by the LED is introduced into the fiber bundle, and the scattering film behind the fiber beam forms a flat sheet, which can be taken out of the sheet in different ways as the back light of the LCD. THE USE OF LED AS BACK LIGHTING LCD DISPLAY CAN BE USED FOR MOBILE PHONES, LAPTOPS, WITH THE SMALL LCD DISPLAY IN THE WIDESPREAD USE OF ENERGY-EFFICIENT COMMUNICATION PRODUCTS, THERE WILL BE GREATER DEMAND FOR ULTRA-HIGH-BRIGHTNESS LEDS. 
4. Solid light 
The practicalization and commercialization of all-color ultra-high-brightness LEDs, so that lighting technology is facing a new revolution, by a number of ultra-high brightness red, blue, green three-color LED made of solid lighting can not only emit wavelength continuously adjustable various colors, but also can emit brightness up to dozens to 100 candlelight white to become a lighting source. Recently, Japan's Niya Corporation, using its InGaN blue light LED and fluorescence technology, has introduced a white-light solid light-emitting device with a color temperature of 6500K and an efficiency of 7.5 lumens per watt. For incandescent and LED solid lamps with the same luminous brightness, the latter consumes only 10% to 20% of the former, incandescent lamps generally have a life of no more than 2,000 hours, and LED lamps have a lifetime of tens of thousands of hours. This kind of solid light source with small size, light weight, good orientation, energy saving, long life and resistance to all kinds of harsh conditions will certainly impact the traditional light source market. Although the cost of this new type of lighting solid light source is still high, it can be applied to some special occasions such as mining, diving, rescue, lighting of military installations, etc. In the long run, if the production scale of ultra-high-brightness LEDs is further expanded and costs are further reduced, its advantages in energy saving and long life are sufficient to compensate for its high price disadvantage. Ultra-bright LEDs will have the potential to become a competitive new electric light source.