LCD buyers should know:
several important parameters that determine the quality of LCD
The main parameters of the LCD include LCD contrast, LCD brightness, LCD display color, LCD signal response time, LCD viewing angle, etc. These parameters are determined by:
1. LCD contrast
The contrast is related to the material of the panel, that is, the control IC, the filter and the alignment film have good contrast quality, but for the average user, the contrast ratio is 350:1, and the contrast requirement for professional users 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.
The contrast is difficult to accurately measure with the instrument, and the sensory judgment can only be made by visual observation under the power-on state.
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 brighter and better, so the number of lamps is directly related to the brightness of the LCD. The early LCD had only two tubes, and later developed into four tubes, and some high-end products had six tubes.
In order to increase the brightness, the four lamps are designed in three forms:
One is to put one tube on each of the four sides, but there is a phenomenon of black shadow in the middle; the second is to arrange the four tubes from top to bottom, although this method eliminates the middle shadow, but The effect is still not very satisfactory; the third is to place the tube in a "U" shape, using only 3 tubes, turning all the tubes into a "U" shape, placed in parallel, thus achieving 6 The effect of the illumination of a tube.
Using 3 tubes to bend them into a "U" shape, not only avoids the black shadow caused by the use of 4 tubes, but also avoids the use of 6 tubes to dissipate a large amount of heat and endanger the life of the display.
2. LCD brightness
The brightness is measured in units of cd/m2. If the brightness is too low, the picture will be dark. At present, the brightness of the TFT type LCD is about 200 cd/m2. For most users, the brightness of 150-200 cd/m2 is sufficient.
3. LCD signal response time
Signal response time is the speed at which the LCD reflects the input signal, usually in milliseconds (ms). According to the inspection of the human eye, when observing the moving picture, the response time is more than 40ms ["1OOO?" 40:25 (frame / s)], there will be hysteresis of the moving image, causing the image to appear afterimage or trailing. The less the response time, the better, but the liquid crystal needs a process from dark to bright, so the signal response time of the LCD should generally be between 1 and 20 ms, and not more than 30 ms.
4. LCD viewing angle
The viewing angle is divided into two aspects: horizontal angle and vertical angle: the horizontal angle is centered on the vertical central axis of the liquid crystal screen, and is moved to the left and right to clearly see the angular scale of the image; the vertical angle is parallel to the liquid crystal screen. The center axis is centered and moves up and down to clearly see the angular extent of the image.
The viewing angle is in "?", which requires a viewing angle of 150? /120? (Horizontal and vertical). The minimum viewing angle is 120? /160? (horizontal/vertical), below this value is not acceptable.
5. LCD display color
Display color refers to the representation of the displayed image in terms of color.
Early LCDs only showed high color (256 colors) in color.
Therefore, many manufacturers use the so-called FRC (FrameRateControl, frame frequency control) technique to enter the color of the picture, but all that is obtained is "pseudo-color". With the continuous advancement of display technology, the current LCD color performance can reach full color (32-bit) mode.
6. LCD screen refresh rate
The screen refresh rate, which is the frequency at which the screen refreshes during the display. It is related to the refresh rate of the picture. Different types of displays have different requirements on the refresh rate.
For CRT monitors, the refresh rate is required to be above 75 Hz. Below this value, the observer will feel the picture flickering. The faster the refresh rate, the better the visual sense of the picture.
For the LCD, the refresh rate is required to be 60Hz. Because in the LCD, each pixel continues to emit light until the non-illuminated signal is sent to the controller, so the LCD does not have a glare caused by charging and discharging. Therefore, when the refresh rate is 60 Hz, the LCD can obtain a good picture.
At present, the LCD screen refresh rate standard is set in the range of 60-75 Hz, the purpose is to replace the CRT display in order to use flexibility and compatibility.
7. LCD resolution
The resolution is usually distinguished by high resolution and low resolution. The resolution has a direct impact on the quality of the image presented by the screen, but different types of displays have different resolution requirements.
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 affecting the resolution. However, the resolution supported by CRT displays is more flexible, and can be displayed regardless of high resolution or low resolution.
The LCD only supports "real resolution", which is high resolution, because the LCD display can only display the best image performance under "real resolution".
The true resolution of the LCD is defined as "fixed-point form", which can be set to the highest when used.
8. LCD resolution
Resolution is one of the most important technical indicators of the display. The higher the resolution, the better the display will be. However, the resolution of the LCD is different from that of the CRT display. It is arranged by pixels in rows and columns. How many pixels per line and how many pixels in each column are set and specified by the manufacturer, so the resolution of the LCD cannot be adjusted arbitrarily. Only when working in the nominal resolution mode, the LCD can achieve the best display.