LCDs or “Liquid Crystal Displays” are nowadays almost indispensable. The term liquid crystal indicates a state that lies between the solid and liquid states. Almost every screen has an LCD installed, for example, as displays on pocket calculators, watches, digital cameras, and also as computer monitors. They work with quasi-liquid crystal chains, which, depending on the voltage applied, rotate the polarization direction of the light and, in connection with polarization foils, produce light and dark points.
How does an LCD Display work?
An LCD display screen basically consists of two panes of glass that have been vapor-deposited with a wafer-thin metal layer. In between, there is a liquid that can rotate the plane of polarization of the incident light. The crystals in the liquid usually consist of rod-shaped molecules whose orientation is changed. If you now apply a voltage to the metal layer, the molecules in the liquid rotate, causing the color of the LCD screen to change.
With LCD, the liquid crystals are located between two transparent electrodes, which are installed between two polarization filters. The filters only let through the light waves that have a certain orientation. When the light goes through the first filter, it is vertically polarized. The crystals are now rotated in such a way that the direction of the light does not change if it does not pass through the second polarization filter, which is rotated by 90 degrees.
The voltage can be used to rotate individual crystals in a different direction via an electric field. This allows a certain amount of light to pass through. Any color can be mixed from the three colors red, green, and blue. The faster the molecules can be rotated, the faster the monitor’s response time. The more pixels there are, the greater the accuracy of the display and the higher the resolution of the monitor.
In general, all LCD displays have a backlight. This is necessary so that you can see something on the screen. Fluorescent tubes were used for this in the past. In the meantime, people have switched to using more cost-efficient LED lighting. In the case of the TFT display ( thin film transistor ), a field effect transistor is applied to each pixel, which controls the voltage at each pixel individually. This gives excellent sharpness and color fidelity. It is easy to see that such complex constructions are expensive.
TFT as a further development of the LCD display
TFTs are a further development of LCD screens that use a different way of driving the pixels. In a TFT, a matrix of active transistors is assigned to each pixel, so each pixel has a completely separate driver and power supply. This technology minimizes interference effects that come into play above all in the course of ever-increasing resolutions (interference voltages, defective pixels, etc.). TFT LCD technology has now become the standard in LCD production.