What are the main parameters of the LCD module?
main parameter
contrast ratio
The control IC, filter, directional film and other accessories used in the manufacture of LCD panel are related to the contrast of the panel. For ordinary users, the contrast of 350:1 is enough, but in the professional field, such a contrast cannot meet the needs of users. Compared with CRT display, it can easily reach 500:1 or higher contrast. Only high-end LCD displays can achieve such a degree. Because it is difficult to measure the contrast accurately with the instrument, you should look at it yourself when selecting it.
Tips: Contrast is very important, which can be said to be a more important indicator for choosing LCD than highlight. When you know that your customers buy LCD for entertainment, you can emphasize that contrast is more important than no bad points. When we watch streaming media, generally the brightness of the film source is not big, but we should see the light and dark contrast of the character scene, and the texture change from gray to black hair, It depends on the level of contrast. Youpai’s VG and VX always emphasize the index of contrast. The VG910S is 1000:1 contrast. When we compared this model with a Samsung dual head video card, the Samsung LCD was obviously better than the Samsung LCD. If you are interested in it, you can try it. The 256 level gray scale test in the test software can see more small gray grids when you look up at it, that is, the contrast is good!
brightness
Liquid crystal is a kind of substance between solid and liquid, which cannot emit light by itself. It needs additional light sources. Therefore, the number of lamps is related to the brightness of the LCD. The earliest liquid crystal display only has two lamps. Up to now, the lowest popular type is also four lamps, and the high-end type is six lamps. The four lamp tube design is divided into three placement forms: one is that there is one lamp tube on each of the four sides, but the disadvantage is that there will be black shadow in the middle. The solution is to arrange the four lamps horizontally from top to bottom. The last is the “U” type placement form, which is actually two lamps produced by two lamps in a disguised form. The six tube design actually uses three tubes. The manufacturer bends the three tubes into a “U” shape and places them in parallel to achieve the effect of six tubes.
Tips: Brightness is also an important indicator. The brighter the liquid crystal, when seen from a distance, stands out from a row of liquid crystal walls. The highlight technologies we often see in CRTs (Youpai called Xianliang, Philips called Xianliang, Benji called Ruicai) all produce brighter effects by increasing the current of the cathode tube and bombarding the phosphor. Such technologies are generally purchased at the expense of the image quality and the life of the display, All products using this technology are bright by default, and can only be implemented by pressing a button. Click 3X to play the game; Press one again to turn to 5X light to watch the video disc. He looks at the video disc and it becomes blurred. If he wants to see the text, he has to return to the normal text mode honestly. In fact, this design is to let everyone not use the highlight. The principle of LCD display brightness is different from that of CRT. They are realized by the brightness of the backlight tube behind the panel. So there are many lamp tubes to be designed, In the early days, when we sold liquid crystals, we told others that liquid crystals were three, so it was amazing. But at that time, Chimei CRV developed a six lamp technology, which actually turned the three tubes into a “U” shape and became the so-called six tubes; This six lamp design, coupled with the strong light emission of the lamp itself, makes the panel very bright. VA712 is the representative of this kind of masterpiece in Youpai; However, all highlighted panels will have a fatal injury. The screen will leak light. This term is rarely mentioned by ordinary people. Personally, I think it is very important. Light leak means that under a completely black screen, the liquid crystal is not black, but turns white and gray. Therefore, good liquid crystals do not always emphasize brightness, but more emphasis on contrast. Youpai’s VP and VG series do not focus on brightness, but on contrast!
Signal response time
The response time refers to the response speed of the LCD to the input signal, that is, the response time of the LCD from dark to light or from light to dark, usually in milliseconds (ms). To make this clear, we should start from the perception of human eyes on dynamic images. There is a phenomenon of “visual residue” in the human eye, and high-speed moving pictures will form a short impression in the human brain. Animations, movies, and the latest games are based on the principle of visual residue, so that a series of gradual images can be displayed in front of people quickly and continuously to form dynamic images. The screen display speed that people can accept is generally 24 frames per second, which is the origin of the movie’s 24 frames per second playback speed. If the display speed is lower than this standard, people will obviously feel the pause and discomfort of the screen. According to this indicator, the display time of each screen should be less than 40ms. In this way, for the LCD, the response time of 40ms becomes a barrier, and displays below 40ms will show obvious “tailing” or “shadow”, which makes people feel chaotic. If you want the image to be smooth, you need to achieve a speed of 60 frames per second.
I use a simple formula to calculate the number of pictures per second under the corresponding reaction time as follows:
Response time 30ms=1/0.030=about 33 frames per second
Response time 25ms=1/0.025=about 40 frames per second
Response time 16ms=1/0.016=about 63 frames per second
Response time 12ms=1/0.012=about 83 frames per second
Response time 8ms=1/0.008=about 125 frames per second
Response time 4ms=1/0.004=about 250 frames per second
Response time 3ms=1/0.003=about 333 frames per second
Response time 2ms=1/0.002=about 500 frames per second
Response time 1ms=1/0.001=1000 frames per second
Tips: We have learned the relationship between the response time and the number of frames through the above content. From this point of view, the shorter the response time, the better. At that time, when the LCD market was just launched, the lowest acceptable response time was 35ms, mainly products represented by EIZO. Later, BenQ’s FP series was launched to 25ms, which was almost imperceptible from 33 frames to 40 frames. The real qualitative change was 16MS, which displayed 63 frames per second to meet the requirements of movies and general games. Therefore, 16MS was not outdated. With the improvement of panel technology, BenQ and Youpai began to compete for speed, and Youpai went from 8MS, It was released to 1MS in 4 milliseconds. It can be said that 1MS is the terminus of the LCD speed debate. For game enthusiasts, fast 1MS means that the shooting method of CS will be more accurate, at least psychologically. Such customers will recommend VX series monitors. However, we should pay attention to the text difference between grayscale response and full-color response. Sometimes, the grayscale 8MS and full-color 5MS may mean the same thing, just as we used to say when we sold CRT that the dot pitch was. 28, LG insisted that it was. 21, and the horizontal dot pitch was ignored, In fact, what the two sides said is that LG has recently developed a 1600:1 sharpness, which is also a concept hype. How many screens are basically used, and how can only LG achieve 1600:1, while everyone stays at the 450:1 level? At first, consumers have clearly understood the meaning of sharpness and contrast, just like AMD’s PR value, which is meaningless
viewing angle
The viewing angle of liquid crystal is a headache. When the backlight passes through the polarizer, liquid crystal and orientation layer, the output light has directivity. That is to say, most of the light is emitted vertically from the screen, so when you look at the LCD from a larger angle, you cannot see the original color, or even can only see all white or all black. To solve this problem, manufacturers also started to develop wide-angle technology. There are three popular technologies, TN+FILM, IPS (IN-PLANE-SWITCHING) and MVA (MULTI-DOMAIN VERTICAL alignment).
TN+FILM technology is to add a layer of wide-angle compensation FILM on the original basis. This compensation film can increase the viewing angle to about 150 degrees, which is a simple and easy method and is widely used in LCD. However, this technology cannot improve the contrast, response time and other performance. TN+FILM may not be the best solution for manufacturers, but it is indeed the cheapest solution. Therefore, most Taiwanese manufacturers use this method to build 15 inch LCD monitors.
IPS (IN-PLANE SWITCHING) technology claims that it can make the upper, lower, left and right viewing angles reach a greater 170 degrees. Although IPS technology increases the viewing angle, using two electrodes to drive the liquid crystal molecules requires more power, which will increase the power consumption of the liquid crystal display. In addition, the response time of driving liquid crystal molecules in this way will be relatively slow.
The principle of MVA (MULTI-DOMAIN VERTICAL ALIGNMENT) technology is to add protrusions to form multiple visible areas. The liquid crystal molecules are not arranged vertically in static state. After the voltage is applied, the liquid crystal molecules are arranged horizontally, so that light can pass through each layer. MVA technology improves the viewing angle to more than 160 degrees, and provides shorter response time than IPS and TN+FILM. This technology was developed by Fujitsu, and Qimei (a subsidiary of Qimei in mainland China) and Taiwan Youda are authorized to use this technology. Youpai’s VX2025WM is the representative of this kind of panel. The horizontal and vertical viewing angles are 175 degrees, basically without blind spots, and it also promises that there are no highlights; The viewing angle is divided into parallel and vertical viewing angles. The horizontal angle is centered on the vertical central axis of the LCD, moving left and right to clearly see the angle range of the image. The vertical angle takes the parallel central axis of the display screen as the center, and moves up and down to clearly see the angle range of the image. The visual angle is expressed in “degrees”. A common way of marking is to directly mark the total horizontal and vertical range, such as 150/120 degrees. The lowest visual angle is 120/100 degrees (horizontal/vertical). It is unacceptable if it is lower than this value. It is better to reach 150/120 degrees or above.
