What Is The Difference Between LED And LCD

- Aug 18, 2018-

   

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LED applications can be divided into two categories: one is LED single-tube applications, including backlight LEDs, infrared LEDs, etc.; the other is LED display. At present, there is still a certain gap between China and LED in the manufacture of LED basic materials, but As far as LED displays are concerned, China's design and production technology levels are basically in line with international standards.

The LED display is a display device consisting of an array of light emitting diodes. It adopts low-voltage scanning drive, which has the characteristics of low power consumption, long service life, low cost, high brightness, less failure, large viewing angle and long visible distance.



The original text of the LCD display is Liquid Crystal Display, which is composed of the first letter of each word. Chinese is often called "liquid crystal flat panel display" or "liquid crystal display". The working principle is to use the physical characteristics of the liquid crystal: the arrangement becomes orderly when energized, so that the light can easily pass; when the power is not energized, the arrangement is disordered, and the light is blocked, and the simple point is that the liquid crystal blocks like a gate or allows light to penetrate. The advantages of LCD are: Compared with CRT display, the advantages of LCD mainly include zero radiation, low power consumption, small heat dissipation, small size, accurate image restoration, sharp character display and so on. There are several basic pointers for purchasing LCD: High brightness: The higher the brightness value, the more natural the picture will be, and the fog will not fog. The unit of brightness is cd/m2, which is the candle per square meter. Low-order LCD brightness values are as low as 150 cd/m2, while high-end displays can be as high as 250 cd/m2. High contrast: the higher the contrast, the more vivid the color, and the more stereoscopic. Conversely, the contrast is low, the color is poor, and the image becomes flat. The difference in contrast values is quite large, ranging from as low as 100:1 to as high as 600:1 or even higher. Wide viewing range: The visual range is simple, referring to the clear range that can be seen in front of the screen. The larger the viewing range, the easier it is to see. The smaller the viewer, the more likely the viewer will not be able to see the picture as soon as the viewer changes the viewing position. The visual range algorithm is a clear range of angles from the middle of the screen to the top, bottom, left and right directions. The larger the value, the wider the range is naturally, but the range in the four directions is not necessarily symmetrical. When up and down, left and right symmetry, some manufacturers will add the angle values of the two sides, marked as horizontal: 160 °; vertical: 160 °; may also be separately labeled left / right: ± 80 °; up / down: ± 80 °. The single angle of some LCD models is even 40°~50°. Fast signal response time: Signal response refers to the time that the system responds to the display after receiving the indication of the keyboard or mouse. Signal response is very important for animation and mouse movement. This phenomenon generally occurs only on LCD liquid crystal displays, and CRT conventional CRT displays do not have this problem. The faster the signal response time, the easier it is to handle the job. One of the methods of observation is to move the mouse quickly (that is, the mouse continuously indicates to the system, and the system continuously responds to the display). On a general low-level LCD display, the cursor disappears during rapid movement. I don't see it until the mouse is positioned, and it will not appear again after a short period of time. In the normal speed action, the movement process will clearly see the mouse movement trace. The VE500's ultra-fast signal response time is as fast as 16ms (milliseconds), so that the cursor moves without time difference, the movement process is clear and easy to see, and it does not cause work troubles.


 



LED light emitting diode features.


LEDs must be super bright luminescent materials, and bright height (UHB) refers to LEDs with luminous intensity up to or exceeding 100mcd, also known as candela (cd) LEDs. The development of high-brightness A1GaInP and InGaN LEDs is progressing rapidly, and has reached the performance level that conventional materials GaA1As, GaAsP, and GaP cannot achieve. 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 was put into practical use. In the same year, Toshiba developed InGaA1P 573nm yellow-green ultra-high brightness LED with a normal light intensity of 2cd. In 1994, Japan Nichia Corporation developed InGaN 450nm blue (green) color ultra-high brightness LED. At this point, the three primary colors of red, green, blue, and orange and yellow LEDs required for color display have reached the candela-level luminous intensity, achieving ultra-high brightness and full color, and making the outdoor full color of the luminous tube. The display becomes a reality. The brightness of the light has been higher than 1000mcd, which can meet the needs of outdoor all-weather and full-color display. The LED color large screen can express the sky and the ocean to realize three-dimensional animation. A new generation of red, green and blue ultra-high brightness LEDs have achieved unprecedented performance.

The outdoor screen pixels are currently composed of a plurality of single-tube LEDs of three primary colors of red/green/blue, and the conventional finished products have two structures of a pixel tube and a pixel module. The pixel size is mostly 12-26 mm, and the pixel composition is: 2R/3R/4R for monochrome, 1R2YG/1R3YG/1R4YG for pseudo color, and 2R1G1B for true color.

Outdoor screen system design principles (content is not described)

△ structural design principles

△ brightness and color basis

△ Reliability design principles

△Safety design principles

△ Easy management and operability design principles

Screen installation method

△ Wall-mounted: the display is placed against the wall and fixed to the wall. This method is a common method and is easy to implement.

△ sitting vertical: the display stands on the platform. This method is the easiest to implement, and this type of installation should be preferred when conditions permit.

△ mosaic: the display is embedded in a wall frame. This method is rare. If the wall is not deep enough, it must be considered for maintainability.

△ Side-mounted: that is, the two sides of the display are stressed, and the side is hung between the two buildings or columns. This method is often used for the screen suspension of the open space, and the two columns are built according to the suspension requirements of the screen.

Display control system

The Dacheng display control system consists of two parts: the acquisition/transmission subsystem and the receiving/gray processing subsystem. The front end is the VGA feature output interface of the computer or the multimedia card with digital component output. The transmission is super five-type twisted pair. Realized, the back end is an electronic display unit. The acquisition/transmission subsystem acquires 24 Bits true color signals at a frame rate of no less than 60 frames per second, and smoothly writes them to the built-in display buffer in a dual memory alternate operation, in the central processing unit. Under the control, the weight conversion of the gray scale is completed, and the difference is LVDS to the super five type twisted pair channel. The super five twisted pair realizes the connection between the acquisition/transmission subsystem and the receiving/gray processing subsystem to complete the signal transmission. In the case of no relay, the longest transmission distance can reach 300 meters.

Grayscale implementation description

The Dacheng Receive/Grayscale Processing Subsystem receives 24 Bits true color signals from the Super Category 5 twisted pair, with weights of 20, 21, 22, 23, 24, 25, 26, 27, and eight for each primary color. The weight component is controlled by the CPLD to realize 256-level gray scale control signals. In the video receiving circuit, the storage circuit, the high-speed writing circuit, and the display control scanning circuit, anti-interference processing is performed, and the display frequency of 150 Hz is refreshed, so that the stability and real-time performance are extremely strong, and the real 24-bit is guaranteed. True color effect.

The number of colors that can be produced by different combinations of 256 gray levels of the three primary colors of red, green and blue is: 256 × 256 × 256 = 16777216 colors (ie 16M color)

Nonlinear gamma correction

The video signal is designed to meet the lighting and electrical characteristics of a television set and can be played on a television or on a display. If the TV signal is not corrected, severe color distortion will occur. Therefore, we must perform nonlinear γ correction on the front end of the input video signal, and the corrected chromaticity space will be significantly improved. Corresponding to the LED large screen, the physical brightness is directly proportional to the gray value. If it is not corrected, it obviously cannot meet the requirements of color reproduction. The specific display effect is: the low level gray level jumps greatly, and the advanced gray level is unclear. . As we all know, the human eye's perception of light intensity is non-linear. When the light is weak, the light intensity is doubled, and the human eye feels more than double the enhancement. When the light is strong, the light intensity is doubled, and the human eye feels the enhancement. It is less than double, so it is necessary to make the gray scale nonlinear transformation, so that the time interval is small when the gray scale is low, and the time interval is high when the gray scale is high. Therefore, in order to ensure the complete restoration of the LED large screen color, anti-gamma correction must be performed. After correction, its characteristics are similar to those of the CRT. We can clearly see that the grayscale-corrected display will appear to have a clear texture, strong layering, soft brightness, and a smooth transition between light and dark.

Technical guarantee of white balance, color deviation and color richness of true color screen

White balance means that when each primary color reaches the highest level of brightness, the white color deviation which is visually excellent outside the certain distance is 6500K, which means that the brightness of the LED light-emitting tube, especially the red light-emitting tube, changes with temperature. a phenomenon. The existence of color deviation indicates that a display screen that achieves white balance at a certain temperature will lose balance due to changes in operating temperature, or the entire display will play after a period of time due to uneven temperature distribution within the screen. "Flower face" phenomenon. The company has a comprehensive solution to the problems caused by the color deviation of the true color display, which can effectively ensure the color richness and consistency of the true color display.

Intelligent monitoring and protection system

The intelligent monitoring system is composed of various sensors, monitoring systems and control computers. It is used to monitor the working environment parameters of the display screen, control the relevant protection system in time, ensure the normal operation of the display screen, and the performance parameters do not shift. The protection system includes: a heat dissipation system, a waterproof system, and a lightning protection system for the distribution system.

controlling software

The normal operation of the display system requires the support of related software. Our software designers have created a powerful and easy-to-use software configuration system through careful preparation and combination. In the software system, according to the different functions of the software, we classify them into two categories: one is the display control software, which mainly completes the playback and switching control of text, animation and video images, which are the basic functions of the display. Software; another type of content editing software is mainly used for creative production and graphic editing, which can make the display content of the display constantly updated and transformed.


 



LCD is divided into STN TFT TFD, etc.

1. What is STN?


  STN (SuperTwistedNematic) is an electric field that changes the arrangement of liquid crystal molecules that are originally twisted more than 180 degrees to change the optical rotation state. The applied electric field changes the electric field by means of progressive scanning. During the process of repeatedly changing the voltage of the electric field, the recovery process of each point is repeated. It is slower and thus produces afterglow. The two biggest differences between STN and TFT are that TFT performance is better than STN, but STN saves power compared to TFT.


  2. What is TFT?


  TFT (ThinFilmTransistor) refers to a thin film transistor, meaning that each liquid crystal pixel is driven by a thin film transistor integrated behind the pixel, so that high-speed, high-brightness, high-contrast display screen information can be achieved. One of the LCD color display devices, which is close to the CRT display, is the mainstream display device on laptops and desktops. Each pixel of the TFT is controlled by a TFT integrated on itself, which is an active pixel. Therefore, not only can the speed be greatly improved, but the contrast and brightness are also greatly improved, and the resolution is also at a very high level.


  3. What is TFD?


  The progress of mobile phones is still going on. In this case, people have higher requirements for LCD performance. The following are important performance characteristics of future mobile phone color LCDs: (1) high image quality; 2) low power consumption; (3) Ability to process moving images; 4) Compact structure; Epson Co., Ltd. has commercialized an active dot matrix LCD-D-TFD (digital thin film diode) and has become a major digital camera manufacturer. one. One of the important reasons is that low power consumption (characteristics of D-TFD) and high image quality/high response speed (characteristics of active dot matrix LCD) meet the requirements of digital cameras. By applying new technologies with high image quality, low power consumption and more compact structure to this D-TFD, we have achieved the above four requirements for the next generation of mobile phones at a high level. This type of LCD is called "MD-TFD".


  4. What is the difference between TFT, STN and TFD LCD?


  The display screen used by the mobile phone has three types: STN mode, TFD mode, and TFT mode. Among them, the best image quality is the TFT method, and most of the displays used in notebook computers are of this type. However, although the TFT is beautiful in appearance and consumes a large amount of power, it has the disadvantage that the battery is not durable for the mobile phone. Although the STN method is the worst in terms of image quality, it has the advantages of low power consumption and low cost. The TFD is positioned just in the middle of the TFT and STN. Although the image quality is slightly inferior to TFT, it consumes less power than TFT.