Most of the LCD technology is based on TN, STN and TFT technology, so we will discuss their operation principles from these three technologies. TN type LCD technology can be said to be the most basic LCD, and after that other types of LCD can also be said to be based on TN type as the original point to improve. Similarly, its operation principle is also simpler than other technologies, please refer to the picture below. The figure represents the simple structure of the TN type liquid crystal display, including the vertical and horizontal direction of the polarizing plate, with fine grooves in the direction of the film, liquid crystal material and conductive glass substrate. The principle of its imaging is to place liquid crystal material in two attached optical axis vertical polarizing plate of transparent conductive glass between the liquid crystal molecules will be aligned to the direction of the fine grooves of the film in order of rotational arrangement, if the electric field is not formed, the light will be smooth from the polarizing plate into the direction of rotation of the liquid crystal molecules, and then from the other side of the shoot out. If the two pieces of conductive glass after energized, between the two pieces of glass will cause an electric field, which in turn affects the arrangement of liquid crystal molecules between them, so that the molecular rods to be twisted, the light will not be able to penetrate, and then cover the light source. The phenomenon of contrast between light and darkness is called twisted nematic field effect (TNFE). Liquid crystal displays used in electronic products are almost all made with the principle of the twisted nematic field effect, and STN-type displays appear to be similar, as shown below, but the difference is that the liquid crystal molecules of the TN twisted nematic field effect rotate the incident light by 90 degrees, whereas the STN super-twisted nematic field effect rotates the incident light by 180 to 270 degrees. It is important to note here that the simple TN LCD itself has only two cases of light and dark (or black and white), and there is no way to do color changes. And STN LCD involves the relationship between liquid crystal materials, as well as the interference phenomenon of light, so the display of the color tones are mainly light green and orange. But if in the traditional monochrome STN LCD plus a color filter (color filter), and any pixel of the monochrome display matrix (pixel) is divided into three sub-pixels (sub-pixel), respectively, through the color filter to display the red, green and blue primary colors, and then through the ratio of the three primary colors of the reconciliation, you can also display the color of the full-color mode. In addition, TN-type LCD monitors, if the larger the display screen, the screen contrast will appear poor, but by STN's improved technology, it can make up for the lack of contrast.
TFT-type LCD is more complex, the main components include: fluorescent tube, light guide plate, polarizer, filter plate, glass substrate, directional film, liquid crystal material, thin mode transistor and so on. First of all, the LCD must first use the backlight, that is, fluorescent tubes to project a light source, which will first pass through a polarizing plate and then pass through the liquid crystal, then the arrangement of liquid crystal molecules to change the angle of light penetrating the liquid crystal. The light then has to pass through a color filter and another polarizer in front of it. Therefore, we only need to change the value of the voltage to stimulate the liquid crystal can control the final appearance of the light intensity and color, and then can be changed in the LCD panel with different shades of color combinations.