Liquid crystal display (LCD) is a flat and thin display device, composed of a certain number of color or black and white pixels, placed on a light source or reflecting ambient light.

The main principle of the liquid crystal display is under the action of an electric field, using the change of the alignment direction of the liquid crystal molecules to change (modulate) the light transmittance of the external light source, complete the electro-optical conversion, and then use the different excitations of the R, G, and B three primary color signals , through the red, green, and blue three primary color filter films, the color reproduction in the time domain and space domain is completed.

Structure:

Each pixel of a liquid crystal display is composed of the following parts: a layer of liquid crystal molecules suspended between two transparent electrodes (indium tin oxide), and two polarizing filters whose polarization directions are perpendicular to each other on the outside of both sides. Without the liquid crystal between the electrodes, the light passing through one of the polarizing filters would be completely perpendicular to the polarization of the second polarizer, and thus completely blocked. But if the polarization of light passing through one polarizing filter is rotated by the liquid crystal, it can be filtered through the other polarization.

Liquid crystal molecules are easily affected by an external electric field to generate induced charges. Adding a small amount of charge to the transparent electrode of each pixel or sub-pixel generates an electrostatic field, and the molecules of the liquid crystal will be induced by the electrostatic field to induce charges and generate electrostatic torsion, which will change the original rotation arrangement of the liquid crystal molecules, and therefore change the magnitude of the rotation of the passing ray. Change a certain angle so that it can pass through the polarizing filter.

Before an electric charge is applied to the transparent electrodes, the alignment of the liquid crystal molecules is determined by the alignment of the electrode surfaces, which act as seeds for the crystals. In the most common TN liquid crystal, the upper and lower electrodes of the liquid crystal are arranged vertically. The liquid crystal molecules are helically arranged, and the polarization direction of the light passing through a polarizing filter is rotated after passing through the liquid crystal plate, so that it can pass through another polarizing plate. During this process a small portion of the light is blocked by the polarizer, which appears gray from the outside. After the charge is added to the transparent electrode, the liquid crystal molecules will be almost completely aligned in parallel with the direction of the electric field, so the polarization direction of the light passing through a polarizing filter is not rotated, so the light is completely blocked. At this point the pixel looks black. By controlling the voltage, the degree of distortion of liquid crystal molecular arrangement can be controlled, so as to achieve different gray scales.

Some liquid crystal displays turn black under the action of alternating current. The alternating current destroys the helical effect of the liquid crystal. After the current is turned off, the liquid crystal display becomes brighter or transparent. This type of liquid crystal display is commonly found on notebook computers and cheap liquid crystal displays. Another type of liquid crystal display that is often used in high-quality liquid crystal displays or large-scale liquid crystal televisions is that when the power is turned off, the liquid crystal display is in an opaque state.

In order to save power, the liquid crystal display adopts the method of multiplexing. In the multiplexing mode, the electrodes at one end are connected in groups, and each group of electrodes is connected to a power supply, and the electrodes at the other end are also connected in groups. On the one hand, the grouping design ensures that each pixel is controlled by an independent power supply, and the electronic device or the software driving the electronic device controls the display of the pixel by controlling the on/off sequence of the power supply.

The indicators for verifying LCD monitors include the following important aspects: display size, response time (sync rate), array type (active and passive), viewing angle, supported colors, brightness and contrast, resolution and aspect ratio, and Input interfaces (such as visual interfaces and video display arrays).