The liquid crystal display (LCD) is based on the principle of placing the liquid crystal between two pieces of conductive glass, driven by the electric field between the two electrodes, causing the liquid crystal molecules to twist to the electric field effect, in order to control the light source transmission or masking function, to produce light and dark changes between the power on and off, so as to display the image. If a color filter is added, the image can be displayed in color. When the glass substrate is not added to the electric field, the light passes through the polarizing plate and follows the liquid crystal to do a 90-degree twist, through the bottom polarizing plate, the liquid crystal panel displays white (Figure 1-3). (-1 left); when an electric field is applied to the glass substrate, the liquid crystal molecules change their alignment, and the light passes through the gaps in the liquid crystal molecules to maintain the original direction and is blocked by the polarizing plate below so that the light is absorbed and cannot penetrate, and the liquid crystal panel displays black (Figure 1-3-1 right)). The liquid crystal display is based on the presence or absence of this voltage so that the panel achieves a display effect.

TFT is short for "Thin Film Transistor", which generally refers to thin-film liquid crystal display, but actually refers to the thin-film transistor (matrix) - which can be "active" or "passive". "The control of individual pixels on the screen is what is known as an active matrix TFT. So how exactly is an image created? The basic principle is very simple: the display screen is composed of many pixels that can emit any color of light, as long as the control of each pixel to display the corresponding color can achieve the purpose. In TFT LCD generally uses backlight technology, in order to accurately control the color and brightness of each pixel, it is necessary to install a switch similar to blinds after each pixel, when the "blinds" open, light can come through, and "blinds". "When it's closed, no light can come through. Of course, in practice, technically it is not as simple as what I just said, as shown in Figure 1-3-2: a finished TFT display, generally consists of a sandwich layer, each layer of this sandwich layer is roughly a polarizer, glass substrate, color filter, ITO electrodes, etc. Between these two layers is the liquid crystal layer, polarizer, color filter, ITO electrodes, and so on. Between these two layers is the liquid crystal layer, polarizer, the color filter determines how much light can pass through and what color light is generated. The liquid crystal layer is located between the two layers of glass substrates. On the upper glass substrate, there are FED transistors, while the lower layer is a common electrode, they work together to generate a precisely controlled electric field, the electric field determines the arrangement of liquid crystal. We all know the three primary colors, so each pixel on the display needs to be composed of three similar basic components introduced above, which control the three colors of red, green, and blue respectively. Currently, the most commonly used is the Twisted Nematic TFT LCD, the following figure is an explanation of the basic working principle of this type of TFT display.

There are grooves on both the upper and lower layers, where the upper grooves are arranged vertically and the lower layer is arranged horizontally. When no voltage is applied to the liquid crystal in the natural state, the light emitted from the luminescence map distorted to the column TFT display operating principle schematic layer through the sandwich layer, the 90-degree distortion will occur, so that the lower layer can pass through smoothly.

When a voltage is added between the two layers, an electric field is created and the liquid crystals are aligned vertically, so the light does not twist - and as a result, the light cannot pass through the lower layer.

The TFT pixel architecture is shown in the figure, color filters are divided into red, green and blue according to the color, which are arranged on the glass substrate to form a group. In other words, if a TFT monitor supports 1280×1024 resolution, at least 1280×3×1024 sub-pixels and transistors are needed. For a 15-inch TFT display is about 0.0188 inches (equivalent to 0.30mm), and for an 18.1-inch TFT display is 0.011 inches (equivalent to 0.28mm).

For more confidence on TFT LCD click here.

Liquid Crystal Display Visualization Principle