The brightness of TFT LCD, measured in cd/m2, is the product of the brightness of the backlight and the transmittance of the display. To increase the brightness of TFT LCD, the common practice is to increase the brightness of backlight. However, this LCD design strategy also brings side effects that the temperature of backlight will be increased, the cost will be increased and many other quality and reliability issues will also occur. Therefore, the best design countermeasure is to improve its transmittance.
To improve the transmittance of TFT LCD, we can improve the transmittance of TFT LCD from the aspects of pixel opening rate, LCD transmittance, polarizer transmittance and CF transmittance. Transmittance design of TFT LCD is a comprehensive result of pixel and material design, which involves a wide range of aspects and many parameters. One of the main tasks of LCD high brightness design is to effectively balance the relationship between the various parameters that affect and finally determine the transmittance value.
The factors that restrict the improvement of transmittance can be roughly summarized into two aspects: quality and cost. The PPI value is relatively higher in high-quality products (resolution is higher in same display size), but if the pixel opening rate is low, and the transmittance is correspondingly low. In order to improve the color reproduction ability of TFT LCD, CF's chromaticity domain is required to be large. However, increasing the chromaticity domain through CF countermeasures will result in the decrease of CF transmittance. Similarly, CF and polarizer contrast and transmittance are also contradictory. In terms of design, in order to obtain high-quality LCD products with low flicker and low cross point, it is often necessary to reduce the impedance of the distribution line by increasing the width of the pixel distribution line, which will reduce the pixel opening rate and thus reduce the transmittance. Under different LCD display modes, transmittance levels are different. The transmittance of IPS display and VA display is lower than that of TN display, but viewing angle of IPS display and VA display is larger. In order to improve the viewing angle, a high-cost compensation film needs to be adopted in TN display. The design with low transmittance of LCD can be done conservatively. Although it has advantages in yield rate, it will increase the cost of materials by using DBEF or other brightening measures.
In the complex factors restricting transmittance of TFT LCD, different transmittance design will bring different adverse effects. To design an ideal TFT LCDs with high brightness, the designer needs to fully understand the transmittance factors related to LCD.