Important Optical Factors of TFT-LCD
2.Contrast Ratio (CR)
3.Response Time (RT)
8.Measurement of optical parameters
1. Viewing Angle：
Viewing Angle generally refers to the angle covered by CR ≥10, the angle between the viewing direction and the normal direction of the display.
The larger the number of Viewing angles, the smaller the grayscale inversion of the view from different angles, and the better the experience. In general, the viewing angle of LCD panels such as IPS/VA/LTPS is better than the traditional TN panel. However, at present, TN panels are increasingly using wide viewing angle polarizer technology to compensate for the lack of viewing angle.
The following figure shows the viewing angle of the TN panel without the wide viewing angle polarizer technology.
2.Contrast Ratio (CR)：
The Ratio of the maximum brightness value (all white) divided by the minimum brightness value (all black) is the Contrast Ratio (CR), and the larger the brightness value is, the brighter the color will be.
For example, if a TFT-LCD monitor displays a full-white (255) image with an actual brightness value of 200cd/㎡ and a full-black image with an actual brightness of 0.5cd/㎡ , The contrast ratio is 400:1.
CR = L255/L0 (Center Point)
Base on the same white/black brightness of LCD display, the higher the contrast, the more distinct the image hierarchy.
3.Response Time (RT)：RT = Tr + TfL
Tr refers to the response time of the LCD when the voltage rises to a stable level (the time required for the change of light transmittance from 10% to 90% after pressure).
TF refers to the voltage drop to a stable LCD reaction time (after the pressure of light transmission from 90% time required to change to 10%).
When the voltage is applied to the electrode of the LCD, the light (brightness) passing through the LCD will change. The reaction time from its change to the stable time is called the light’s reaction time（response time), which divided into Tr and TF.
Tr refers to the reaction time of LCD when the voltage rises to a stable state (the time required for the light penetration rate to change from 10% to 90% after pressure). Tf refers to the reaction time of LCD when the voltage drops to a stable state(the time required for the light penetration rate to change from 90% to 10% after pressure).
The unit of Response Time (RT) is ms, and the larger the value of response time is, the slower the response time will be. Of course, the smaller the value of response time is, the less the phenomenon of tail dragging will occur when the user watches the moving pictures.
Theoretically, the number of frames per second that can be displayed with different response times:
16 ms =1/0.016= 62.5 frames per second
8 ms =1/0.008= 125 frames per second
5 ms =1/0.005= 200 frames per second
4 ms =1/0.004= 250 frames per second
The left picture is for LCD monitor with faster response times and the right is for products with normal response times.
The transmittance is the ratio of the brightness of the light passing through the Cell Panel to the brightness of the backlight.
The higher the transmittance, the higher the brightness of the light passing through the Cell Panel based on the same backlight brightness. In other words, high transmittance means high brightness.
Luminance refers to the visible brightness of an object, depending on how much light is transmitted. Symbol L, unit cd/m2
Luminance(L) = backlight brightness (nit) * panel transmittance (%)
If the luminance is too low, the screen will be darker; and the display will be clearer when high luminance. However, if the screen luminance is too high, the eyes will be tired of too long.
Color is represented by chromaticity and brightness together. Chromaticity reflects the color character besides brightness, namely tonal with saturation, determined by the composition of the three primary colors (R, G, B).
NTSC refers to the degree of bright colors. If the RGB primary colors are more bright, the display can display a wider range of colors. The color range can be displayed with the primitive color range divided by the color range specified by NTSC.
8.Measurement of optical parameters
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