Differences between LEDs and LCD

Source: Internet
Author: User

LED is the abbreviation of light emitting diode.

Led applications can be divided into two categories: one is the single-tube led applications, including back-light LED, infrared LED, and so on; the other is the LED display. Currently, there is still a certain gap between China and the International in the manufacture of basic led materials. However, for the LED display screen, China's design and production technology level is basically in line with international standards.

An LED display is a display device consisting of LEDs. It is driven by low-voltage scanning and has the following features: low power consumption, long service life, low cost, high brightness, less fault, large angle of view, and long visual distance.

The original text of the LCD display is liquid crystal display, which consists of the first letter of each word. The Chinese name is "LCD flat display" or "LCD display 」. The working principle is to use the physical characteristics of the liquid crystal: The arrangement becomes orderly during power-on, so that the light passes easily; the arrangement becomes chaotic when no power-on is enabled, and the light passes through is prevented, to put it simply, the liquid crystal can block or let the light penetrate like a gate. LCD has the following advantages: Compared with CRT display, LCD has the following advantages: Zero radiation, low power consumption, low heat dissipation, small size, precise image restoration, and sharp character display. Choose LCD, there are several basic pointers: High Brightness: the higher the brightness value, the more beautiful the picture, not haze. The unit of brightness is cd/m2, that is, the candle per square meter. The low-level LCD brightness value is as low as 150 cd/m2, while the high-level display can be up to cd/m2. High contrast: the higher the contrast, the more colorful and saturated, and the more three-dimensional. On the contrary, the contrast is low, the color is poor, and the image will become flat. The comparison values are quite different, ranging from 600 to: 1, or even higher. Broad visual range: In simple terms, it refers to the clear range that can be viewed on the screen before the screen. The larger the visual range, the easier it is to see. The smaller the visual range, the more you can see, the more you can see. The algorithm of the visual range is to clearly define the angle range of the image from the center, bottom, left, and right. The larger the value, the wider the range, but the range of the four directions is not necessarily symmetric. When the upper and lower sides are symmetric, some manufacturers will add the angle values on both sides, marked as horizontal: 160 °; Vertical: 160 °; may also be marked as left/right: + 80 °; top/bottom: + 80 °. The single angle of some LCD models, even 40 ° ~ 50 °. Fast signal response time: the time when the system responds to the display after receiving the instructions from the keyboard or mouse, which is calculated and processed by the CPU. The signal reaction is very important for animation and mouse movement. Generally, it only occurs on LCD display, while the conventional CRT display does not. The faster the signal response time, the more convenient the job processing. One of the ways to observe is to move the mouse quickly (that is, the mouse continuously instructs the system, and the system constantly reflects the signal to the display) on a low-level LCD display, when the cursor moves rapidly, it disappears and appears again after the cursor is positioned and not moved for a short period of time, the moving process also clearly shows the mouse movement marks. However, ve500's ultra-fast signal response time is as short as 16 ms (milliseconds), which makes the cursor move without time lag. The moving process is clear and easy to see without causing any troubles.

LED features.

LEDs must use super-bright materials. The bright height (UHB) refers to LEDs with luminous intensity reaching or exceeding MCD, also known as camdra (CD) LEDs. The Development of High Brightness a1gaindium and InGaN led has been very rapid and has reached the performance level impossible for conventional materials such as gaa1as, gaasp and gap. In 1991, Toshiba Corporation of Japan and HP Corporation of the United States developed the ingaa1p 620nm orange Ultra-High Brightness LED. In 1992, the ingaa1p590nm yellow Ultra-High Brightness LED was put into practice. In the same year, Toshiba developed the ingaa1p 573nm yellow-green ultra-high-brightness LED, with a forward-to-light intensity of up to 2cd. In, Japanese company Japan developed a blue (green) ultra-high-brightness LED with nm InGaN. At this point, the three colors of red, green, blue, orange, and yellow LEDs required for color display have reached the kandra-level luminous intensity, achieving ultra-high brightness and full color, make the outdoor full color display of luminous tubes a reality. The luminous intensity is higher than MCD, which can meet the outdoor all-weather and full-color display needs. The large screen of LED color can express the sky and ocean, and realize 3D animation. The new generation of red-green and blue-ultra-high-Brightness LEDs achieve unprecedented performance.

At present, the exterior screen pixels are composed of several single-tube LEDs in red, green, and blue colors. The commonly used products are two structures: the pixel barrel and the pixel module. The pixel size is generally 12-26mm, and the pixel Composition: The monochrome is mostly in the form of 2R/3R/4R, 1r2yg/1r3yg/1r4yg, and 2r1g1b. Design Principles of the out-of-room screen system scheme (content is not described)

△ Structure Design Principles

△Brightness and color matching basis

△Reliability Design Principles

△ Security design principles

△Ease of management and operational design principles

Screen Installation Method

△Wall mounting: the display screen is mounted to the wall and fixed to the wall. This method is common and easy to implement.

△ Sit-up: that is, the display screen is sitting on the platform. This method is the easiest to implement. This installation method should be preferred when conditions permit.

△ Mosaic: displays are embedded in a wall frame. This method is rare. If the depth of the wall is not deep enough, the maintainability should be considered.

△ Side hanging: Stress on both sides of the display screen, side hanging between two buildings or columns. This method is usually used for screen suspension of an empty site. The two columns are built based on the suspension requirements of the screen.

Display Control System

The Dacheng display control system consists of the acquisition/sending subsystem and the receiving/grayscale processing subsystem. Its front-end is the VGA feature output interface of the computer or a multi-media card with digital component output, transmission is implemented by cat5e twisted pair wires, and the backend is an electronic display unit. The acquisition/sending sub-system collects 24 bits real-color signals at a frame rate of no less than 60 frames per second, and smoothly writes the signals to its own display cache in the way that the dual storage device works alternately, the gray-scale weight conversion is completed under the control of the central processing unit, and the LVDS is used to differential to cat5e Twisted Pair Channels. Cat5e twisted pair wires connect the collection/sending subsystem with the receiving/grayscale processing subsystem to complete signal transmission. The maximum transmission distance is 300 meters without relay.

Grayscale implementation description

The Dacheng receiving/grayscale processing subsystem receives 24 bits true-color signals from cat5e twisted pair wires with weights of 20, 21, 22, 23, 24, 25, 26, and 27, respectively, each base color has eight weight components, which are controlled by CPLD to implement a 256-level grayscale control signal. Anti-interference processing is performed in the video receiving circuit, storage circuit, high-speed writing circuit, and display control scanning circuit, and the display screen refresh frequency is Hz. Therefore, it has strong stability and real-time performance, ensure the true 24-digit effect.

The numbers of colors produced by different combinations of red, green, and blue are 256x256x256 = 256 colors (16 m colors) nonlinear Gamma Correction.

The video signal is designed to meet the luminous characteristics and electrical characteristics of the TV. It can be played on the TV or on the display. If the TV signal is not corrected, serious color distortion will occur. Therefore, we must perform nonlinear Gamma Correction on the front end of the input video signal, and the color space after correction will be significantly improved. Corresponding to the LED large screen, the physical brightness is proportional to the gray value. If no correction is made, it obviously cannot meet the requirements of color restoration. The specific display effect is: low-level gray jump is very large, the advanced gray level is unclear. As we all know, the human eye's perception of light intensity is non-linear. When the light intensity is low, the light intensity doubles, and the human eye feels more than doubled. When the light intensity is strong, the light intensity doubles, the human eyes feel less than twice the enhancement, so we need to perform non-linear transformation on the gray scale, so that the low gray scale distance is small, and the high gray scale distance is large. Therefore, in order to ensure the complete color reproduction of the LED large screen, the anti-Gamma Correction must be performed. After correction, the characteristics of the correction are similar to those of the CRT. We can clearly see that after gray-scale correction, the displayed image will have a clear texture, a strong sense of brightness, soft brightness, and smooth light and shade transition.

Technical guarantee of white balance, color deviation and color richness of the real color screen

White Balance refers to when each base color reaches the highest level of brightness, A white color deviation with a color temperature of KB outside of a certain distance is a phenomenon in which the brightness of the LED light-emitting tube, especially the red light-emitting tube, changes with the temperature. The existence of Color Deviation indicates that a screen with the white balance produced and debugged at a specific temperature will be out of balance as the operating temperature changes, or, due to the uneven temperature distribution in the screen, the entire display screen will show a "face" phenomenon after playing for a period of time. The company has a comprehensive set of solutions for 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 consists of various sensors, monitoring systems, and control computers. It is used to monitor the parameters of the display working environment, control the relevant protection systems in a timely manner, and ensure that the display works normally, the performance parameter does not have a large offset. Protection systems include: heat dissipation system, waterproof system, and power distribution system lightning protection system.

Control Software

The normal operation of the display system must be supported by relevant software. Our software designers have carefully compiled and combined to create a powerful and easy-to-use software configuration system. In this software system, according to different functions of the software, we classify them into two categories: one is the display control software, it mainly controls the playback and switching of text, animation, and video images. They are the basic software for the display. The other is the content editing software, which is mainly used for creative production and graphic editing, they can update and change the display content of the display.

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