Basic Introduction to LCD Displays

Origin

LCD (full name Liquid Crystal Display). At the end of the 19th century, an Austrian botanist discovered liquid crystal, a substance that combines the fluidity of liquid and the arrangement characteristics of crystal. Under the action of electricity, the arrangement of liquid crystal molecules will change, affecting its optical properties. The scientific community calls this phenomenon the electro-optical effect.

British scientists relied on this principle to create the first liquid crystal display, or LCD display, in the last century. The world's first liquid crystal display device appeared in the early 1970s and was called TN-LCD (twisted nematic) liquid crystal display. Then, with the development of the times, screen manufacturing and production have become more and more mature. It is these great scientists who allow us to enjoy a visual feast. 

Internal structure

Don't look at the thin layer of the screen. Although it is small, it has all the internal organs. The internal structure contains a lot, mainly composed of a liquid crystal panel and a backlight panel. Here, Xiaozhan will give you some knowledge. The LCD screen is actually a non-active light-emitting electronic device. It does not have the characteristics of light emission itself. The two structures must correspond to each other to obtain the display performance.

The liquid crystal panel is composed of a polarizing film, a glass substrate, a black matrix, a color filter, a protective film, a common electrode, a calibration layer, a liquid crystal layer (liquid crystal, a spacer, a sealant), a capacitor, a display electrode, a prism layer, a light diffusion layer, etc., which will be increased or decreased according to the use environment of the liquid crystal panel. The backlight module includes an illumination light source, a reflector, a light guide plate, a diffuser, a brightening film (prism sheet) and a frame. Therefore, the production environment of the liquid crystal panel is also very strict. It mainly relies on automated production equipment for precise production, and a dust-free workshop to ensure functional use. It is also required to undergo multiple tests and inspections before it can be considered a qualified product.

Working principle

Liquid crystal is a type of organic compound between solid and liquid. Under normal temperature conditions, it exhibits both the fluidity of liquid and the optical anisotropy of crystal. It will become a transparent liquid when heated and a crystalline turbid solid when cooled.

Under the action of the electric field, the liquid crystal molecules will change in arrangement, thereby affecting the change in the intensity of the incident light beam passing through the liquid crystal. This change in light intensity is further manifested as a change in brightness through the action of the polarizer. Based on this, the light can be changed to dark by controlling the electric field of the liquid crystal, so as to achieve the purpose of information display. Therefore, the role of the liquid crystal material is similar to a small "light valve". Because there are control circuits and drive circuits around the liquid crystal material. When the electrodes in the LCD generate an electric field, the liquid crystal molecules will be distorted, so that the light passing through them will be refracted regularly, and then filtered by the second layer of polarizer and displayed on the screen.

Selection suggestion

Brightness

The maximum brightness of the LCD is usually determined by the backlight source. Technically, high brightness can be achieved, but this does not mean that the higher the brightness value, the better, because a display with too high brightness may cause eye damage to the viewer. LCD is a substance between solid and liquid. It cannot emit light by itself and needs additional light sources. Therefore, the number of lamps is related to the brightness of the LCD.

Resolution

Resolution refers to the number of pixels displayed per unit area. The physical resolution of the LCD is fixed and unchanged. It is more complicated to implement in the LCD. It must be simulated by calculation to simulate the display effect. The actual resolution does not change.

Color

The most important thing about LCD is of course the color expression. We know that any color in nature is composed of three basic colors: red, green, and blue. Most manufacturers produce LCDs with 6 bits for each of the three basic colors, or 64 degrees of expression, so each independent pixel has 262,144 colors.

If you want a better color experience, you can use FRC technology to simulate the full-color picture, that is, each of the three primary colors can reach 8 bits, or 256 degrees of expression, so each independent pixel has up to 16,777,216 colors.

Contrast

Contrast is defined as the ratio of the maximum brightness value (full white) divided by the minimum brightness value (full black). The control IC, filter, and directional film accessories selected during LCD manufacturing are related to the contrast of the panel.

Response time

Response time refers to the response speed of the LCD to the input signal, that is, the response time of the liquid crystal from dark to bright or from bright to dark, usually in milliseconds. The smaller this value, the better the experience. If the response time is too long, the LCD may have a tail shadow dragging problem when displaying dynamic images.

Viewing Angle

The viewing angle of a liquid crystal display is symmetrical left and right, but not necessarily up and down. When the incident light from the backlight passes through the polarizer, liquid crystal and orientation film, the output light has a specific directional characteristic. In most cases, the light emitted from the screen has a vertical direction. If we watch a completely black screen from a very oblique angle, we may see white or color distortion. Generally speaking, the up and down angles are less than or equal to the left and right angles.

Viewable Area

The size indicated on the LCD monitor is consistent with the actual screen range that can be used. The viewing area refers to the maximum range of graphics that your monitor can display.