Domestic products are Hisense, Skyworth, Changhong, TCL and Konka.
LED is short for light emitting diode.
LED applications can be divided into two categories: one is LED single-tube applications, including backlight LED, infrared LED, etc. The other is an LED display. At present, there is still a certain gap between China and the international in the manufacturing of LED basic materials, but as far as LED display screen is concerned, the technical level of design and production in China is basically in sync with the international level.
LED display screen is a display device composed of light emitting diodes. Adopting low-voltage scanning drive, it has the characteristics of low power consumption, long service life, low cost, high brightness, few faults, large viewing angle and long line of sight.
The original text of LCD display is LCD display, which consists of the first letter of each word. In Chinese, it is usually called "LCD flat panel display" or "LCD display". Its working principle is to use the physical characteristics of liquid crystal: after electrifying, the arrangement becomes orderly, which is convenient for light to pass through; When there is no electricity, the arrangement is chaotic, which hinders the passage of light. Simply put, let the liquid crystal block or let the light pass like a gate. The advantages of liquid crystal display are: compared with CRT display, the advantages of liquid crystal display mainly include zero radiation, low power consumption, small heat dissipation, small size, accurate image restoration, clear character display and so on. There are several basic guidelines for purchasing LCD: high brightness: the higher the brightness value, the brighter the picture and no fogging. The unit of brightness is cd/m2, that is, one candle per square meter. The brightness value of low-order LCD is as low as 150 cd/m2, while that of high-order display can be as high as 250cd/m2. High contrast: The higher the contrast, the brighter, more saturated and stereoscopic the color will be. On the contrary, the contrast is low, the color is barren, and the image will become flat. The difference of comparative value is quite large, as low as 100: 1, as high as 600: 1 or even higher. Wide visual range: In short, the visual range refers to the clear range that can be seen in front of the screen. The larger the visual range, the easier it is to see; The smaller it is, the picture may not be clear as long as the viewer changes the viewing position slightly. The algorithm of visual range is a clear angle range from the middle of the picture to the top, bottom, left and right directions. The larger the value, the wider the range, but the range in four directions is not necessarily symmetrical. When the upper, lower and left sides are symmetrical, some manufacturers will add the angle values on both sides and mark them as horizontal:160; Vertical:160; It may also be separately marked as left/right: 80; Up/down: 80. The single angle of some LCD models even reaches 40 ~ 50. Fast signal response time: signal response refers to the time it takes for the system to receive the instructions from the keyboard or mouse, which are processed by the CPU and then reflected on the display. Signal response is very important for animation and mouse movement. Generally speaking, this phenomenon only occurs on liquid crystal displays, while CRT traditional kinescope displays do not have this problem. The faster the signal response time, the more convenient the job processing. One way to observe is to move the mouse quickly (that is, the mouse keeps giving instructions to the system, and the system keeps responding to signals to the display). On the general low-order LCD display, when the cursor moves quickly, it will disappear in the process and reappear until the mouse is positioned and motionless for a short time; In the general speed action, you can also clearly see the traces of mouse movement during the movement. However, the ultra-fast signal response time of VE500 is as high as 16ms (milliseconds), which makes the cursor move without time difference, and the moving process is clear and easy to see, which does not bring trouble to the operation.
Characteristics of LED light emitting diode.
The LED shall be made of ultra-bright luminescent materials, and the brightness height (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 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.
At present, outdoor screen pixels are composed of several single-tube LEDs with three primary colors of red/green/blue, and commonly used finished products have two structures: pixel tube and pixel module. The pixel size is 12-26 mm, and the pixel composition is 2R/3R/4R for monochrome,1r2yg/1r3yg/1r4yg for pseudo color, and 2r1g1.
Design principle of outdoor screen system scheme (content not described)
△ Structural design principles
△ Brightness and color matching basis
△ Reliability design principle
△ Safety design principle
△ Design principle of easy management and operation
Installation mode of screen body
△ Wall-mounted: that is, the display screen is backed against the wall and fixed on the wall. This method is very common and easy to implement.
△ Sit up straight: that is, the display screen sits on the platform. This method is the easiest to realize, and this installation method should be preferred when conditions permit.
△ Mosaic: The display screen is embedded in a wall frame. This method is rare. If the depression depth of the wall is not enough, its maintainability must be considered.
△ Side hanging type: that is, the two sides of the display screen are stressed and hung between two buildings or columns. This method is often used to hang the screen in the open air, and two columns are built according to the hanging requirements of the screen.
Display control system
Dacheng display and control system consists of acquisition/sending subsystem and receiving/gray processing subsystem. Its front end is the VGA characteristic output interface of computer or multimedia card with digital component output, and transmission is realized through super five twisted pairs, and the back end is the display unit of electronic display screen. The acquisition/transmission subsystem collects 24-bit true color signals at a frame rate of not less than 60 frames per second, and writes them into its own display buffer in the mode of alternating operation of dual memories. Under the control of the central processor, the weight transformation of gray scale is completed, and it is divided into over five pairs of twisted pair channels through LVDS. The ultra-five twisted pair realizes the connection between the acquisition/sending subsystem and the receiving/gray processing subsystem, and completes the signal transmission. Without relay, the longest transmission distance can reach 300 meters.
Gray level realization description
Dacheng receiving/gray processing subsystem receives 24-bit true color signals from super-five-class twisted pair with weights of 20, 2 1, 22, 23, 24, 25, 26 and 27 respectively. Each primary color has eight weight components, and the 256-level gray control signal is realized by CPLD control. Anti-interference processing is carried out in video receiving circuit, storage circuit, high-speed writing circuit and display screen control scanning circuit. The refresh frequency of display screen is 150Hz, which has strong stability and real-time performance, and ensures the real 24-bit true color effect.
Different combinations of 256 gray levels of the three primary colors of red, green and blue can produce 256× 256× 256 =1677 7216 colors (i.e. 16M colors).
Nonlinear gamma correction
The design of video signal conforms to the lighting and electrical characteristics of TV and can be played on TV or monitor. If the TV signal is not corrected, it will produce serious color distortion. Therefore, we must carry out nonlinear gamma correction on the front end of the input video signal, and the chromaticity space after correction will be obviously improved. Corresponding to the LED large screen, the physical brightness is directly proportional to the gray value. If it is not corrected, it is obviously unable to meet the requirements of color reproduction. Specifically, the display effect is that the low-order gray scale jumps greatly and the high-order gray scale is not clear. As we all know, human eyes' perception of light intensity is nonlinear. In weak light, the light intensity is doubled, and the perception of human eyes is more than doubled. Under strong light, the intensity of light is doubled, but the enhancement felt by human eyes is less than doubled. Therefore, it is necessary to carry out nonlinear transformation of gray scale to make the interval between low gray scale and high gray scale smaller. Therefore, in order to ensure the complete color reproduction of LED large screen, anti-gamma correction must be carried out, and its characteristics will be similar to CRT after correction. We can clearly see that the gray-scale corrected display screen will have the effects of clear texture, strong layering, soft brightness and smooth light-dark transition.
Technical guarantee of white balance, color difference and color richness of true color screen
White balance means that when each primary color reaches the highest level of brightness, it visually presents a white deviation of an excellent temperature of 6500K at a certain distance, that is to say, the brightness of LED light emitting tubes, especially red light emitting tubes, changes with temperature. The existence of color difference shows that the white balance display screen produced and debugged at a specific temperature will lose its balance with the change of working temperature, or the temperature distribution in the screen will be uneven, which will make the whole display screen appear "face painting" after playing for a period of time. Our company has a comprehensive solution to the problems caused by color deviation of true color display screen, which can effectively ensure the color richness and consistency of true color display screen.
Intelligent monitoring and protection system
The intelligent monitoring system consists of various sensors, monitoring system and control computer, which is used to monitor the working environment parameters of the display screen, and control relevant protection systems in time to ensure the normal operation of the display screen and no big deviation in performance parameters. Protection system includes: cooling system, waterproof system, lightning protection system of distribution system, etc.
control software
The normal operation of the display screen system must be supported by relevant software. Our company's software designers have created a powerful and easy-to-operate software configuration system through careful compilation and combination. In this software system, according to the different functions of software, we divide it into two categories: one is display control software, which mainly completes the playback and switching control of text, animation and video images, and they are the basic software for display screen work; The other is content editing software, which is mainly used for creative production and graphic editing. They can constantly update and change the display content of the display screen.
Liquid crystals are divided into STN TFT TFD and so on.
What is 1.STN?
STN (Super Twisting Machine) changes the optical rotation state by changing the arrangement of liquid crystal molecules above 180 degrees with an electric field. The applied electric field changes the electric field by scanning line by line. In the process of repeatedly changing the electric field voltage, the recovery process of each point is slow, resulting in afterglow. The two biggest differences between STN and TFT are that the performance of TFT is better than STN, but STN saves power than TFT.
2. What is 2.TFT?
Tft (thin film transistor) refers to the thin film transistor, which means that each liquid crystal pixel is driven by the thin film transistor integrated behind the pixel, so that it can display screen information with high speed, high brightness and high contrast. It is one of the best LCD color display devices at present, and its effect is close to CRT display. It is the mainstream display device on notebook computers and desktops. Each pixel of a TFT is controlled by a TFT integrated on itself and is an active pixel. Therefore, not only the speed can be greatly improved, but also the contrast and brightness are greatly improved, and the resolution has reached a very high level.
3. What is TFD?
The progress of mobile phones continues. In this case, people have higher requirements for the performance of LCD. The following are the important performance characteristics of color LCD for mobile phones in the future: (1) high image quality; 2) low power consumption; (3) being able to process moving images; 4) compact structure; Epson has commercialized an active dot matrix LCD-D-TFD-TFD (Digital Thin Film Diode) and become one of the major manufacturers of digital cameras. One of the important reasons is that low power consumption (characteristic of D-TFD) and high image quality/high reaction speed (characteristic of active dot matrix LCD) meet the requirements of digital cameras. By applying the new technology with high image quality, low power consumption and more compact structure to this D-TFD, we have achieved the above four requirements of the next generation mobile phone at a high level. This kind of LCD is called "MD-TFD".
4.4 What's the difference? TFT, STN, TFD LCD screen
There are three kinds of display screens used in mobile phones: STN mode, TFD mode and TFT mode. Among them, the best picture quality is TFT mode, and most of the display screens used in notebook computers are of this type. However, although the picture of TFT is beautiful, it consumes a lot of power, so for mobile phones, it has the disadvantage that the battery is not durable. STN mode has the worst picture quality, but it has the advantage of low power consumption and low cost. TFD is located between TFT and STN. Although the picture quality is slightly worse than TFT, it consumes less power than TFT.