LED display screen problem

LED panel): LED is the abbreviation of light emitting diode. It is a display mode by controlling semiconductor light-emitting diodes. Generally, its appearance consists of many small lights, usually red, which are turned on and off to display characters. A display screen for displaying text, graphics, images, animations, quotations, videos, video signals and other information.

LED display screen is divided into graphic display screen and video display screen, both of which are composed of LED matrix blocks. The graphic display screen can display Chinese characters, English texts and graphics synchronously with the computer; The video display screen is controlled by a microcomputer and has pictures, words and images. It plays all kinds of information in a real-time, synchronous and clear way, and can also display two-dimensional and three-dimensional animations, videos, televisions, VCD programs and live scenes. LED display screen has bright colors, strong stereoscopic impression, static as oil painting and moving like a movie, and is widely used in public places such as finance, taxation, industry and commerce, posts and telecommunications, sports, advertising, factories and mines, transportation, education system, stations, docks, airports, shopping malls, hospitals, hotels, banks, securities markets, construction markets, auction houses, industrial enterprise management, etc.

LED display screen can display changing numbers, characters and graphic images; It can be used in both indoor and outdoor environments, and has incomparable advantages over projectors, TV walls and LCD screens.

The widespread attention and rapid development of LED are inseparable from its own advantages. These advantages are summarized as follows: high brightness, low working voltage, low power consumption, miniaturization, long life, impact resistance and stable performance. The development prospect of LED is very broad, and it is developing towards higher brightness, higher weather resistance, higher luminous density, higher luminous uniformity, reliability and full color.

[Edit this paragraph] Second: Review of LED display development in the past 30 years.

In the1970s, the earliest homogeneous red, yellow and green LEDs with low luminous efficiency GaP and GaAsP have been applied to indicator lamps, digital and text displays. Since then, LED has entered a variety of application fields, including aerospace, aircraft, automobiles, industrial applications, communications, consumer products and so on. Covering all sectors of the national economy and thousands of households. By 1996, the global sales of LED have reached several billion dollars. Although LED has been limited by color and luminous efficiency for many years, GaP and GaAsP LED have many advantages, such as long life, high reliability, low working current and compatibility with TTL and CMOS digital circuits, so they have been ignored by users. In recent ten years, high brightness and full color have been the frontier topics of LED materials and device technology research. Ultra-high brightness (UHB) refers to the LED whose luminous intensity reaches or exceeds 100mcd, also known as Candeira LED. The development of high brightness A 1GaInP and InGaN LED has made rapid progress, and now it has reached the performance level that conventional materials GaA 1As, GaAsP and GaP can't. 199 1 In 2001, Toshiba Corporation of Japan and Hewlett-Packard Company of the United States developed InGaA 1P 620nm orange ultra-high brightness LED, and 1992 InGaA 1p590nm yellow ultra-high brightness LED was put into practical use. In the same year, Toshiba developed InGaA 1P 573nm yellow-green ultra-high brightness LED with normal light intensity of 2cd. 1994 InGaN 450nm blue (green) ultra-high brightness LED was developed by Niya Company of Japan. At this point, all the red, green, blue, orange and yellow LEDs required for color display have reached the Candeira-class luminous intensity, achieving ultra-high brightness and full color, making the outdoor full-color display of light-emitting tubes a reality. The development of LED in China began in 1970s, and the industry appeared in 1980s. There are about 100 enterprises in China, 95% of which are engaged in back packaging production, and almost all the required molds are imported from abroad. Through several "five-year plans" of technical transformation, technical research, the introduction of foreign advanced equipment and some key technologies, China's LED production technology has taken a step forward.

Second, the performance of ultra-high brightness LED:

Compared with GaAsP-GaP LED, ultra-high brightness red A 1GaAsLED has higher luminous efficiency, and the lumen efficiency of transparent substrate (TS) A 10lm/w is close to that of red GaAsP-GaP LED 10 times. Ultra-high brightness InGaAlP LED provides the same colors as GaAsP-GaP LED, including green yellow (560 nm), light green yellow (570 nm), yellow (585 nm), light yellow (590 nm), orange (605 nm), light red (625 nm) and deep red (640 nm). Compared with other LED structures and incandescent light sources, the luminous efficiency of transparent substrate A 1GaInP LED is1kloc-0/m/w for absorption substrate (AS) and 20 1m/w for transparent substrate (TS), which is higher than GAASP in the wavelength range of 590-626 nm. In the wavelength range of 560-570, it is 2-4 times higher than GaAsP-GaP LED. Ultra-high brightness InGaN LED provides blue light and green light, with the wavelength range of 450-480 nm for blue light, 500nm for blue-green light, and 520nm for green light. Its lumen efficiency is 3-151m/w. At present, the lumen efficiency of ultra-high brightness LED has exceeded that of incandescent lamp with filter, which can replace incandescent lamp with power within 1w, and LED array can replace incandescent lamp with power within 150w. For many applications, incandescent lamps use filters to obtain red, orange, green and blue, while ultra-high brightness LEDs can obtain the same color. In recent years, ultra-high brightness LEDs made of AlGaInP and InGaN materials combine multiple ultra-high brightness LED chips, and various colors can be obtained without filters. Include red, orange, yellow, green and blue. At present, their luminous efficiency has surpassed incandescent lamps and is close to fluorescent lamps. The luminous brightness is always higher than 1000mcd, which can meet the needs of outdoor all-weather and full-color display. LED color large screen can represent the sky and the ocean and realize three-dimensional animation. A new generation of red, green and blue ultra-high brightness LED has achieved unprecedented performance.

Third, the application of ultra-high brightness LED:

1. information indicator

Car signal indication: car indicator lights are mainly direction lights, taillights and brake lights outside the car; The interior of the car is mainly the lighting and display of various instruments. Compared with traditional incandescent lamps, ultra-high brightness LED has many advantages and has a broad market in the automobile industry. LED can withstand strong mechanical impact and vibration. The average service life of MTBF is several orders of magnitude higher than that of incandescent bulbs, which is much higher than that of automobiles. Therefore, the LED brake light can be packaged as a whole without considering maintenance. Compared with incandescent bulbs with filters, the transparent substrate Al. GaAs and AlInGaP LED have high lumen efficiency, which makes LED brake lights and direction lights work at lower driving current, and the typical driving current is only 65,438+0/4 of that of incandescent bulbs, thus reducing the driving distance of automobiles. Lower electric power can also reduce the volume and weight of the automobile internal wiring system, and at the same time reduce the internal temperature rise of the integrated LED signal lamp, allowing the lens and cover to use low-temperature resistant plastics. The response time of LED brake lights is 100ns, which is shorter than that of incandescent lamps, leaving more response time for drivers and improving the safety of driving. The illuminance and color of the external indicator light of the car are clearly defined. Although the automobile interior lighting display is not controlled by the relevant government departments like the external signal lights, automobile manufacturers have requirements on the color and illuminance of led. GaP LED have been used in automobiles. AlGaInP and InGaN LED with ultra-high brightness will replace incandescent lamps in automobiles, because they can meet the requirements of manufacturers in color and illumination. From the price point of view, although LED lamps are more expensive than incandescent lamps, there is no obvious difference in the prices of the two from the perspective of the whole system. With the practical development of ultra-high brightness TS AlGaAs and AlGaInP LED, the price has been declining in recent years, and the decline will be even greater in the future.

Traffic signal indication: Ultra-high brightness LED is used to replace incandescent lamp, and has been used in traffic lights, warning lights and sign lights all over the world. The market is vast and the demand is growing rapidly. According to the statistics of the US Department of Transportation 1994, there are 260,000 traffic lights installed at intersections in the United States, and each intersection must have at least 12 red, yellow, blue and green traffic lights. Many intersections also have some extra change signs and crosswalk warning lights. In this way, there can be 20 traffic lights at each intersection, and they should emit light at the same time. It can be inferred that there are about 654.38+35 billion traffic lights in the United States. At present, using ultra-high brightness LED instead of traditional incandescent lamp to reduce power consumption has achieved remarkable results. The annual power consumption of traffic lights in Japan is about 6.5438+0 million kilowatts. After replacing incandescent lamp with ultra-high brightness led, the power consumption is only 654.38+02% of the original.

The competent departments of various countries should formulate corresponding traffic signal lamp specifications, and stipulate the signal color, minimum illumination, spatial distribution mode of light beams and installation environment requirements. Although these requirements are written according to incandescent lamps, they are basically applicable to the ultra-high brightness LED traffic lights currently in use. Compared with incandescent lamps, LED traffic lights have a longer service life, which can generally reach 10 years. Considering the influence of harsh outdoor environment, it is expected that the service life will be reduced to 5-6 years. At present, the ultra-high brightness AlGaInP red, orange and yellow LEDs have been industrialized, and their prices are relatively cheap. If the traditional red incandescent lamp holder is replaced by a module composed of ultra-high brightness red light emitting diodes, the impact on safety caused by the sudden failure of red incandescent lamps can be minimized. LED traffic signal lamp module is generally composed of multiple groups of LED single lamps connected in series. Take 12 inch red LED traffic light module as an example. In 3-9 groups of LED single lamps connected in series, the number of each group of LED single lamps is 70-75 (2 10-675 LED single lamps in total). When a single LED lamp fails, only one group of signals will be affected, and the other groups will be reduced to.

The main problem of LED traffic signal module is that the interface is still relatively high. Take 12 inch TS-AlGaAs red LED traffic light module as an example. I used it for the first time on 1994, and the cost was $350. By 1996, the cost of the 12 inch AlGaInP LED traffic signal lamp module with better performance is $200. It is predicted that in the near future, the price of InGaN blue-green LED traffic signal module will be comparable to that of AlGaInP. Although the cost of incandescent traffic signal lamp holder is low, it consumes a lot of electricity. The power consumption of an incandescent traffic signal lamp holder with a diameter of 12 inch is 150W, and the power consumption of traffic warning lamps crossing roads and sidewalks is 67W. According to the calculation, the annual power consumption of incandescent traffic lights at each intersection is 18 133KWh, which is equivalent to the annual electricity bill of 65438+. However, LED traffic signal module is very energy-saving. Each 8- 12 inch red LED traffic light module consumes 15W and 20W respectively. The LED signs at intersections can be displayed with arrow switches, and the power consumption is only 9w. According to the calculation, each intersection can save 99 16 kwh per year, which is equivalent to saving 793 dollars of electricity every year. According to the average cost of each LED traffic signal module of $200, the red LED traffic signal module can recover its initial cost after 3 years only by saving electricity, and begin to get economic returns continuously. Therefore, the AlGaInP LED traffic information module currently used is economical in the long run, although the cost is obvious.

2. Large screen display

Large screen display is another huge market for ultra-high brightness LED applications, including monochrome, two-color and full-color display of graphics, characters and numbers. Table 2 lists the various uses of LED display screen. Traditional large-screen active displays generally use incandescent lamps, optical fibers, cathode ray tubes and so on. Passive display generally adopts the method of flop. Table 3 lists the performance comparison of several monitors. LED display screen has always been limited by the performance and color of LED itself. At present, ultra-high brightness AlGaInP, TS-AlGaAs and InGaN LED can provide bright red, yellow, green and blue colors, which can fully meet the requirements of full-color large screen display. The led display screen can be assembled into various structures according to the pixel size, and the diameter of small pixels is generally less than 5 mm One T- 1(3/4) LED lamp is used for monochrome display, and one two-color T- 1(3/4) LED lamp is used for two-color display, while three T- 1 red, green and green LEDs are needed for full-color display. Large pixels are composed of many T- 1(3/4) red, green and blue LED lights. Using InGaN(480nm) blue, InGaN(5 15nm) green and ALGaAS(637nm) red LED lamps as the three primary colors of the LED display screen can provide realistic full-color performance with a wide range of colors, including cyan, green and red. , which basically conforms to the TV color range specified by the International Television Systems Committee (NTSC).

3. Backlighting of LCD.

At least 10% of liquid crystal displays use active light as backlight. Light source can make LCD screen readable in dark environment, and full-color LCD also needs light source. The light sources required for LCD backlight mainly include incandescent bulbs, electroluminescence, cold cathode fluorescence, LED and so on. Table 4 lists them for comparison. Among them, LED is the most competitive in LCD backlight, and new ultra-high brightness AlGaInP, AlGaAs and InGaN LED can provide high-efficiency light emission and a wide range of colors.

There are three main ways for LED to be used for LCD backlight lighting. (1) The simplest thing is to install the LED lamp directly behind the LCD scattering film. Many packaged LED lamps can be used, and a wide beam angle is required to make the axial light uniformity better. You can also use an unpackaged die, generally using GaP LED, but using AlGaInP and TS-AlGaAs LED can work at low current and reduce power consumption. (2) The other way is side light type liquid crystal backlight. A transparent or translucent rectangular plastic block is used as a light guide, which is directly installed behind the LCD scattering film. The back of the plastic block is coated with white reflective material, and LED light is injected from one side of the plastic block, and the other side is made of white reflective material. (3) The light emitted by the LED is guided into the optical fiber bundle, and a flat plate is formed behind the scattering film of the optical fiber bundle, so that the light can be taken out of the flat plate in different ways and used as the backlight of the LCD. LCD with LED backlight can be used in mobile phones and notebook computers. With the wide application of small LCD in energy-saving communication products, the demand for ultra-high brightness LED will be greater.

4. Solid state lighting

The practicality and commercialization of full color ultrasound high brightness led make the lighting technology face a new revolution. The solid lighting lamp composed of a plurality of ultra-high brightness red, blue and green light-emitting diodes can not only emit various colors with continuously adjustable wavelengths, but also emit white light with brightness as high as several tens to one hundred candles as the lighting source. Recently, Niya Company of Japan introduced a white solid-state light-emitting device with a color temperature of 6500K and an efficiency of 7.5 lumens/watt by using its InGaN blue LED and fluorescent technology. Incandescent lamps and LED solid-state lighting lamps with the same luminous brightness only consume 10%-20% of the former, and the life of incandescent lamps generally does not exceed 2000 hours, while the life of LED lamps is tens of thousands of hours. This solid-state light source with small volume, light weight, good directivity, energy saving, long service life and resistance to various harsh conditions will definitely impact the traditional light source market. Although the cost of this new lighting solid light source is still high, it can be used in some special occasions, such as mining, diving, emergency rescue, lighting of military equipment and so on. In the long run, if the production scale of ultra-high brightness LED is further expanded and the cost is further reduced, its advantages in energy saving and long life are enough to make up for its high price disadvantage. Ultra-high brightness LED may become a new competitive electric light source.

[Edit this paragraph] Third: Classification of LED display screens:

1, according to the primary colors can be divided into

Single primary color display: a single color (red or green).

Double primary color display: red and green double primary colors, 256 gray levels, which can display 65,536 colors.

Full-color display screen: Red, green and blue. A full-color display screen with 256 gray levels can display more than16 million colors.

2, according to the display device classification

LED digital display: The display device is a 7-segment digital tube, which is suitable for making clock screens and interest rate screens. And display a digital electronic display screen.

LED dot matrix graphic display screen: The display device is a dot matrix display module composed of many evenly arranged light emitting diodes, which is suitable for playing text and image information.

LED video display screen: The display device consists of many light-emitting diodes, which can display various video files such as videos and animations.

3. Classification by purpose

Indoor display screen: the luminous point is relatively small, generally φ 3 mm-φ 8 mm, and the display area is generally several to ten square meters.

Outdoor display screen: the area is generally tens of square meters to hundreds of square meters, with high brightness, which can work in the sun and has the functions of wind, rain and water prevention.

4, according to the luminous point diameter classification

Indoor screens: φ 3mm, φ 3.7mm, φ 5mm, φ 5mm,

Outdoor screens: φ 10mm, φ 12mm, φ 16mm, φ 19mm, 20mm, φ2 1mm, 22mm, 26mm.

The basic unit of outdoor screen is light-emitting tube. The principle of light-emitting tube is to package a group of red, green and blue light-emitting diodes in a plastic tube to emit light together.

5. Display modes include static, horizontal scrolling, vertical scrolling and page turning display. A single module controls and drives 12 (up to 24) 8×8 lattices, totaling 16×48 lattices (or 32×48 lattices), which is a single MAX72 19 (or similar LED display driving modules such as PS72 19 and HD 722). "Cascading" can form a large display screen with any lattice. Good display effect, low power consumption and lower cost than using MAX72 19 circuit.