LCD screens are divided into two types: regular white and regular black. Regular black screens include LG's IPS screen, Samsung's SPVA screen, and Taiwan's Youda MVA screen, among others. The principle has been explained before, and regular white screens are TN screens, which are commonly used in low-end products such as laptops and home monitors. So why do both types of screens appear black?
One reason is that the transmittance of bare cells (panels without polarizing film) is already very low (ranging from 10% to 10%), and after applying polarizing film, the transmittance needs to be further reduced by 40%. The second reason is because you didn't light up the backlight. The LCD display module is designed like a blackbody and ensures that the light source can only come from backlight, otherwise it can be seen as bright under ambient light, which is a major quality issue and QE will not pass.
Backlight is a type of light emitted by a point light source that is directed in all directions and passes through a light guide plate. The backlight becomes uniform. The light from all directions passes through the polarizing plate and is filtered, allowing it to only pass horizontally through the polarizing plate, while the light from the vertical direction cannot pass through. Liquid crystal materials have optical rotation properties, which can slowly rotate the "horizontal" light to 90 °, 270 °, etc. It can completely become "vertical" and then pass through the filter plate (this TN type liquid crystal phase matching method forms a 90 ° angle between the filter plate and the polarizer plate), with a brightness of 100%; When rotated to 180 °, 360 °, etc., it will be completely impossible to pass through the filter plate with a brightness of 0%; The remaining angle grayscale ranges from 0 to 100%.
At this point, there is only a brightness color between black and white, so every three liquid crystals are grouped together, passing through red, green, and blue filter glass to form a set of three primary colors. These three colors (the proportion is determined by the rotation angle of the liquid crystal) are superimposed into one desired color, forming one pixel. By controlling the magnitude of the voltage, the angle of the liquid crystal twist can be controlled, that is, the brightness obtained through this liquid crystal can be controlled.
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