LCD TV and LCD Display

 

The discovery of LCD Display dates back to 1888 when an Austrian botanist named Reinitzer discovered a special mixture that exhibited properties between solid and liquid states. This unique substance possessed dual characteristics of both solid and liquid materials.It displayed liquid-like mechanical qualities such as flowability, viscosity, and deformation, as well as crystal-like physical properties such as thermal (thermal effects), optical (optical anisotropy), electrical (electro-optic effect), and magnetic (magneto-optic effect). It existed as an intermediate state between solid and liquid, representing a regularly arranged organic compound. Because there was no other title for this substance at the time, it was dubbed "Liquid Crystal." Organic molecules centered on carbon atoms make up the composition of liquid crystals.

Liquid crystals themselves do not emit light. They primarily rely on changes in voltage to generate an electric field, which causes the alignment of liquid crystal molecules to change and display images. The LCD panel consists of two pieces of sodium-free glass sandwiching a layer made up of polarizing plates, a liquid crystal layer, and color filters. The polarizing plates and color filters determine the amount and color of light that can pass through. The liquid crystal is filled between the two well-made planes, and both planes have numerous grooves. Each plane's grooves are parallel, but the grooves on the two parallel planes are perpendicular to each other. Simply put, if the grooves on the back plane are vertical, then the grooves on the front plane are horizontal. The arrangement of liquid crystal molecules between the two planes forms a gradually twisted state in the Z-axis direction at 90 degrees. The backlight source, emitted by a lamp, passes through the backlight plate and reflection film on the back of the LCD screen, generating uniform backlight rays. These rays are distorted in the Z-axis direction by the liquid crystal through the rear layer, allowing them to pass through the front layer. An electric field is formed when a voltage is supplied to the liquid crystal layer, causing the liquid crystal molecules to reorganize, preventing the rays from bending and passing through the front layer, so blocking the light. In summary, applying voltage blocks the light, while without voltage, the light is emitted. Of course, the arrangement of liquid crystals in the LCD display can be changed such that light is emitted when a voltage is applied and blocked when no voltage is applied. However, because LCD screens are almost always lighted, the "applying voltage blocks the light" strategy uses the least amount of energy.

 

Currently, LCD TVs have largely replaced old-style CRT TVs and have become widely used as a new display device. The following is an analysis of the liquid crystal display used in LCD TVs.

TFT-LCD Display Principle Analysis (illustrated with an example): Taking a 1024×768 pixel LCD screen as an example, a backlight source behind the liquid crystal panel projects pure white light. The light passes through the first polarizing film and is filtered into polarized light in the corresponding direction. After passing through the transparent electrodes and the liquid crystal, the liquid crystal molecules' tilt angle and transmittance are controlled by the TFT control circuit. After passing through the liquid crystal, the light passes through the color filters, forming 1024×768×3 beams of RGB primary colors with controlled deflection directions. Through the second polarizing film, the beams of RGB primary colors with controlled deflection directions are filtered into beams of RGD primary colors with controlled intensity. Finally, the projected light is emitted from the screen. By changing the voltage applied to drive the liquid crystal, the intensity, and color of the final light can be controlled, allowing different shades of color combinations to be displayed on the LCD panel.

 

Q: Are there any disadvantages of LCD displays?

 

A: The luminance of LCD displays relies on the backlight source for illumination, and the maximum brightness is determined by the backlight source. In terms of brightness, LCD screens usually maintain a brightness level of 300-500cd/㎡. If you want to increase its screen brightness, you need to increase the brightness of the backlight source. However, this approach has a drawback: excessively increasing the brightness of the backlight source can accelerate its aging and reduce its lifespan, which is one of the fatal flaws.

 

References:

[1] "Liquid crystal and its display principles." Electrical Apparatus, 2004(10), 28-32.

 

[2] Man, Z. "Display principles and technical characteristics of LCD TVs." China New Communications, 2017, 19(19), 147-148.