The main parameters of LCD include contrast, brightness, display color, signal response time, viewing angle, etc. The methods for determining these parameters are:;
1. Contrast
Contrast is related to the material of the panel, that is, the control IC, filter, alignment film and other accessories are of good quality. The contrast is high, but for general users, the contrast ratio is 350:1. For professional users, the contrast ratio should be high. Some. At present, the contrast ratio of high-end LCD has reached 500:1, 600:1, which can fully meet the needs of professional fields.
Contrast is difficult to accurately measure with instruments, and it can only be judged by visual observation when it is turned on.
Since the liquid crystal itself cannot emit light, it needs to be illuminated by an external light source, that is, a lamp tube. The brightness is of course the brighter the better. Therefore, the number of lamp tubes is directly related to the brightness of the LCD. In the early days, LCD had only two upper and lower lamps, and later developed to 4 lamps, and some high-end products had 6 lamps.
In order to improve the brightness, the 4 lamps are designed into three types of placement:
One is to put a lamp on each of the four sides, but there is a black shadow in the middle; the second is to arrange the 4 lamps from top to bottom. Although this method eliminates the black shadow in the middle, The effect is still not very satisfactory; the third is to place the tubes in a "U" shape, using only 3 tubes, turning all 3 tubes into a "U" shape, and placing them in parallel, so that it reaches 6 The illumination effect of a lamp tube.
The use of 3 lamps to dome it into a "U" shape, not only avoids the dark shadows caused by the use of 4 lamps, but also avoids the use of 6 lamps to dissipate a lot of heat and endanger the life of the display.
2. brightness
The brightness is measured in cd/m2. If the brightness is too low, the picture will feel dark. At present, the brightness of TFT LCD is around 200cd/m2. For most users, a brightness of 150~200cd/m2 is sufficient.
3. Signal response time
The signal response time refers to the response speed of the LCD to the input signal, usually in milliseconds (ms). According to the inspection ability of the human eye, when observing the moving picture, if the response time exceeds 40ms [《1o0o? 40:
25(frame/s) ], there will be a lag in the moving image, which will cause the image to appear afterimages or trailing traces. The shorter the response time, the better, but it takes a process for the LCD to turn from dark to bright. Therefore, the signal response time of LCD should generally be between 1 and 20ms, and not greater than 30ms.
4. Viewing angle
The viewing angle is divided into two aspects: the horizontal angle and the vertical angle: the horizontal angle is centered on the vertical central axis of the LCD screen, moving to the left and right, can clear the angle of the hair to the shadow; the vertical angle is the liquid crystal The parallel central axis of the screen is the center, moving up and down, you can clearly see the angle range of the image.
The viewing angle is in units of "?", and the viewing angle is required to reach 150? / 120? (horizontal/vertical). The minimum viewing angle is 120? / 160? (horizontal/vertical), lower than this value is not acceptable.
5. Display color
Display color refers to the representation of the displayed image in terms of color.
Early LCDs can only display high color (256 colors) in terms of color.
Therefore, many manufacturers use the so-called FRC (FrameRateControl, frame rate control) technique to get the color of the screen, but what they get is only "pseudo-color". With the continuous advancement of display technology, the color performance of current LCDs can reach full-color (32-bit) mode.
6. Screen refresh rate
The screen refresh rate is the frequency at which the screen refreshes during the display process. It is related to the refresh rate of the screen, and different types of displays have different requirements for the refresh rate.
For CRT monitors, the refresh rate is required to be above 75Hz, below this value, the observer will feel the screen flicker. The faster the refresh rate, the better the visual perception of the picture.
For LCD, the refresh rate requirement is 60Hz. Because in the LCD, each pixel continues to emit light until the signal that does not emit light is sent to the controller, so the LCD will not have the sparkle caused by constant charging and discharging. Therefore, when the refresh rate is 60Hz, the LCD can get a good picture.
At present, the LCD screen refresh rate standard is set in the range of 60-75Hz, the purpose is to use flexibility and compatibility, and eventually replace the CRT display.
7. Resolution
Resolution is usually distinguished by high resolution and low resolution. The resolution has a direct impact on the quality of the image presented on the screen, but different types of displays have different requirements for resolution.
The image of a traditional CRT display is mainly realized by dots and lines composed of pixels, so the number of pixels is an important factor that affects the resolution. However, the resolution supported by CRT monitors is more flexible, and it can display whether it is a high resolution or a low resolution.
LCD only supports "real resolution", that is, high resolution, because LCD monitors can only show the best effect in the "real resolution".
The true resolution of LCD is defined as "fixed-point form", and it can be set to the highest when in use.
8. Resolution
Resolution is one of the most important technical indicators of a display. The higher the resolution, the better the display. However, the resolution of LCD is different from that of CRT display. It is composed of image points arranged in rows and columns. The number of pixels in each row and the number of pixels in each column are set and specified by the manufacturer, so the resolution of LCD cannot Arbitrary adjustment, LCD can achieve the best display effect only when working in the nominal resolution mode.
