Learn more about LCD displays and their work

Resource Description

When you look at your monitor or screen, you see colored pictures. We already know that the computer thinks in numbers only receiving commands from the CPU.

Thus, what is responsible for the appearance of a variety of color images we interact with? The work is performed by the well-known color Liquid Crystal Display or LCD.

Liquid crystals

Liquid crystals were discovered in 1888 by the Austrian scientist Friedrich Reinitzer. And in 1927, the Russian physicist Vsevolod Frederiks discovered a transition that was named after him and is now widely used in LCD displays. In the 1970s, the SHARP company first introduced a monochrome liquid crystal screen. Liquid crystal displays began to be used in electronic watches, calculators, and measuring instruments. Then, matrix displays began to appear, reproducing black and white images.

In 1987, SHARP developed the first 3-inch color liquid crystal display. What is that? How does an LCD display screen work?

In the 19th century, scientists discovered liquid crystals. Their structure is intermediate between two states of substances - a liquid-like and crystalline solid. There are several phases but in general, the principle of their work is the following: the direction of the liquid crystals situated between glass panels is determined by the corrugation (grooves), which is located on these panels. Therefore, if the location of the corrugation is parallel, then the LCs are located accordingly.


Polarization of light

The work of an LCD or Liquid Crystal Display is based on the polarization of the light flux. In this case, there is a question: what is polarized light?

Light is transverse electromagnetic waves. If a filter is a polarizer, a stretched plastic film with horizontal lines (invisible to the human eye) is placed in the path of the light, all light waves, except horizontal ones, will be blocked, and vice versa. This is how polarized sunglasses work by letting in light equal to their direction and plane.

An LCD has two polarizers. The function of the bottom (or back) polarizer is to transmit a specific directional light, while the function of the front polarizer is to improve the sensitivity and the light itself, allowing the LCD to be seen. If you place the polarizers parallel to each other, according to the principle of one on top of the other, the screen will become as bright as possible. Perpendicularly positioned polarizers block all light, making the screen black. The absence of polarizers means that neither letters nor graphics can be recognized.

How does LCD work?

The work of an LCD is based on the polarization of the light flux. Liquid crystals sift light by passing only certain waves of the light beam with the appropriate polarization axis and remaining opaque to all other waves. Changes in the polarization vector are carried out by liquid crystals depending on the electric field applied to them. In other words, with the help of electricity, you can change the orientation of the crystal molecules and thereby provide an image. Any LCD screen on a computer monitor, laptop, tablet, or TV contains several hundred thousand to several million such cells, fractions of a millimeter in size. They are combined into an LCD matrix and with their help, we can form an image on the surface of a liquid crystal screen.

Almost any LCD display has an active matrix of transistors with the help of which an image is formed: a layer of liquid crystals with light filters that selectively transmit light and a backlight system that is used to display color images and usually consists of LEDs.

An LCD display has several layers, the main of which are two glass panels that contain a thin layer of liquid crystals between them. The panels have grooves that guide the crystals in alignment. The grooves are parallel on each panel, perpendicular between the two panels. In contact with the grooves, the molecules in liquid crystals are oriented in the same way in all cells.

An LCD display screen itself is an array of small segments - pixels. For each pixel, there are 3 transistors, each of which is responsible for one of three colors - red, green, and blue (RGB), and a capacitor that supports the required voltage —Āombines three primary colors for each pixel of the screen, you can get any color. Currently, the most common are liquid crystal TFT (Thin-Film Transistor) displays, which use thin-film transparent transistors in the active matrix. The number of transistors in such displays can reach several hundred thousand. And that is the simplest way to understand the unique way of LCD display organization and work.

Among the advantages of LCD displays are relatively low cost, excellent focusing, very high image clarity, brightness, as well as the absence of color registration errors and screen flickering. The fact is that such displays do not use an electron beam to draw every line on the screen. Among the disadvantages of LCDs are the appearance of dead pixels due to the combustion of transistors, a small number of color shades, uneven brightness of the picture, and often the illumination at the edge of the display is stronger, and a relatively small viewing angle.