Currently, most of the LCD technologies have TN/HTN/STN/FSTN and other TFT technologies as the main axis, so we will discuss the working principle from these technologies.
TN LCD technology is arguably the most basic LCD, and the various other LCDs that have followed can be said to have been improved upon with the TN type as the origin. Again, it works much simpler than other technologies, see the diagram below. The figure shows the simple structure of a TN liquid crystal display, including vertical and horizontal polarizers, an oriented film with fine grooves, liquid crystal material and a conductive glass substrate. The principle of the display is that the liquid crystal material is placed between two pieces of transparent conductive glass and the vertical polarizer is attached to the optical axis. The liquid crystal molecules will rotate and align themselves sequentially according to the direction of the fine grooves of the film. If no electric field is formed, light will enter the polarizer smoothly, the liquid crystal molecules will rotate their direction of travel, and then shoot out the other side. If two pieces of conductive glass is energized, an electric field will be formed between the two pieces of glass, affecting the arrangement of liquid crystal molecules between the two pieces of glass, so that their molecular rods are distorted, and the light will not be able to penetrate, thus blocking the light source. The contrasting light and dark phenomenon thus obtained is known as the twisted nematic field effect, or TNFE (twisted nematic field effect).
Almost all liquid crystal displays used in electronics are made from the principle of the twisted nematic field effect.STN type displays have a similar principle but differ in that the liquid crystal molecules of the TN twisted nematic field effect rotate the incident light by 90 degrees while the STN super twisted nematic field effect rotates the incident light by 180 to 270 degrees. It is important to note here that pure TN LCDs by themselves are only bright and dark (or black and white), and there is no way to do color change. Instead, STN LCDs involve the relationship between liquid crystal materials and the phenomenon of light interference, so the colors of the display are mainly light green and orange. However, if a color filter is added to a conventional monochrome STN LCD, and any pixel of the monochrome display matrix is divided into three sub-pixels, and the three primary colors of red, green and blue are displayed separately through the color filter, the ratio of the three primary colors can be reconciled. It can also display colors in full color mode. In addition, TN-type LCD monitors have poorer screen contrast if the larger the screen is displayed, but the lack of contrast can be compensated for by the improved technology of STN.
TFT-type liquid crystal displays are more complex, and the main components include, fluorescent tubes, light guides, polarizers, filter plates, glass substrates, directional films, liquid crystal materials, and thin-mode transistors. First, the LCD must use a backlight, a fluorescent tube, which projects a light source through a polarizer and then through a liquid crystal in which the molecules are arranged in a way that changes the angle at which the light passes through the liquid. The light must then pass through a color filter and another polarizer in front of it. So, by changing the voltage of the liquid crystal, we can control the intensity and color of the light, and then we can change the color combinations of the different shades on the LCD panel.