Liquid crystal display (LCD) is a kind of display using liquid crystal as material. What is liquid crystal? In fact, liquid crystal is a kind of material between solid and liquid. When heated, it will appear transparent liquid, and when cooled, it will crystallize into chaotic solid. Liquid crystal is an organic compound with regular molecular arrangement. According to the different arrangement of molecular structure, liquid crystals can be divided into three types: Smectic liquid crystals similar to clay, Nematic liquid crystals similar to thin matchstick and Cholesteric liquid crystals similar to cholesterol. The physical properties of these three kinds of liquid crystals are not the same. Nematic liquid crystals of the second kind are used in liquid crystal displays. The molecules are long rods. In the natural state, the long axes of these long rods are roughly parallel.