LCD product types: According to the driving mode of LCD, current LCD products can be classified into two categories: TN/Twisted Nematic, STN/Super Twisted Nematic, and TFT/Thin Film Transistor.
1. The principle of TN industrial LCD display
TN industrial LCD display is filled with liquid crystal between a pair of parallel polarizing plates. The polarization directions of this pair of polarizing plates are perpendicular to each other. Liquid crystal molecules are arranged in multiple layers between polarizing plates. Within the same layer, although the positions of liquid crystal molecules are irregular, their long axis orientation is parallel to the polarizing plate. It is precisely because molecules are arranged in this way that they are called nematic liquid crystals. On the other hand, between different layers, the long axis of liquid crystal molecules continuously twists 90 ° along the parallel plane of the polarizing plate. Among them, the orientation of the long axis of the two liquid crystal molecules adjacent to the polarizing plate is consistent with the direction of the polarized light of the adjacent polarizing plate. It is precisely because of the twisted arrangement of liquid crystal molecules that they are called twisted nematic industrial liquid crystal displays. Once the liquid crystal molecules are charged through electrodes, due to the influence of external voltage, they are no longer arranged in the normal way and instead become in an upright state. The interlayer of industrial LCD displays is attached with two polarizing plates, and the arrangement and transmittance angle of these two polarizing plates are the same as the groove arrangement of the upper and lower layers. Under normal circumstances, when light is irradiated from top to bottom, only one angle of light can penetrate through. It is guided into the groove of the upper interlayer through the upper polarizing plate, and then exits from the lower polarizing plate through the twisted arrangement of liquid crystal molecules, forming a complete path for light penetration. When liquid crystal molecules stand upright, light lines cannot pass through, resulting in black appearing on the display screen. This will result in white when transparent and black when opaque, so that the characters can be displayed on the screen.

2. The principle of TFT industrial LCD displays
The TFT industrial LCD display also adopts a design of filling liquid crystal molecules between two interlayers. It's just that the electrode in the upper layer of TN is changed to a FET transistor, and the lower layer is changed to a common electrode. In terms of light source design, TFT displays adopt a "backlit" illumination method, which means that the hypothetical light source path is not from top to bottom like TN liquid crystal, but from bottom to top. This approach involves installing a fluorescent tube on the back of the liquid crystal. When the light source is illuminated, it first penetrates upwards through the lower polarizing plate and uses liquid crystal molecules to conduct light. Due to the modification of the electrodes in the upper and lower interlayers to FET electrodes and common electrodes, when the FET electrode is conductive, the performance of liquid crystal molecules will change, just like the arrangement of TN liquid crystal. The display purpose is also achieved through shading and transparency. However, the difference is that due to the capacitive effect of FET transistors, they can maintain a potential state. Previously transparent liquid crystal molecules will remain in this state until the next time the FET electrodes are charged and their arrangement is changed. Relatively speaking, TN does not have this characteristic. Once the liquid crystal molecules are not under pressure, they immediately return to their original state, which is the biggest difference in the display principle between TFT liquid crystal and TN liquid crystal.
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