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Basic introduction of TFT LCD part one

Basic introduction of TFT LCD part one

Jan 17, 2023

TFT liquid crystal display principle

The main components of the TFT type liquid crystal display include: polarizing plate (1), glass substrate (2), thin mode transistor (3), alignment film (4), liquid crystal material (5), guide plate (6), color filter Light board (7), fluorescent tube (8), etc. First of all, the liquid crystal display must first use a backlight source, that is, a fluorescent tube to project a light source. These light sources pass through a polarizing plate and then through the liquid crystal. At this time, the arrangement of the liquid crystal molecules changes the angle of light that penetrates the liquid crystal. Then the light must pass through the colored filter film and another polarizing plate in the front. Therefore, we can control the final light intensity and color by changing the voltage value that stimulates the liquid crystal, and then can change the color combination of different shades on the liquid crystal panel.

1. Perspective

When the incident light from the backlight passes through the polarizer, the liquid crystal layer, and the so-called guide film, the output light has specific directional characteristics, that is, most of the light emitted from the screen is in the vertical direction. If we look at a completely white picture from a very oblique angle, we may see black or color distortion. This effect is useful in some situations, but it is undesirable in most applications. Manufacturers have spent a lot of time trying to improve the viewing angle characteristics of liquid crystal displays. Several wide viewing angle technologies have been proposed: IPS (IN-PLANE -SWITCHING, MVA (MULTI-DOMAIN VERTICAL ALIGNMENT), TN+FILM). These technologies can Increase the viewing angle of the liquid crystal display to 160 degrees or more, just like the viewing angle characteristics of the CRT LCD screen. The maximum viewing angle is defined as a viewing angle with a contrast value of at least 10:1 (usually four directions, up/down/left /right).

2. Brightness:

The unit of brightness is cd/m2. For example, 250cd/m2 means that the brightness of 250 candles lit in an area of ​​1 square meter is equal. The best brightness accepted by human eyes is 150 cd/m2. Because the brightness of the display is affected by external light, it is necessary to manufacture a display with a relatively high brightness. The current display with the highest brightness is 450 cd/m2.

The maximum brightness is usually determined by the cold cathode ray tube (backlight source). The brightness value of TFT-LCD is generally 200"250 cd/m2. Although higher brightness can be achieved technically, this does not mean that the higher the brightness, the higher the brightness. Good, because a display that is too bright may hurt the viewer’s eyes.

The maximum brightness of CRT displays is about 100 to 120 cd/m2. It is very difficult to achieve a higher brightness value, because the kinescope gun requires a larger acceleration voltage, and the result of this will cause a higher radiation amount and reduce the life cycle of excited phosphorescence and other two negative effects.

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