A thin, flat electronic visual display that uses the light modulating properties of liquid crystals is known as a liquid crystal display. Direct light is not emitted by LCDs. Displaced cathode ray tube (CRT) displays of LCDs are used in most applications. Two sheets of polarizing material, are used in LCD displays, with a liquid crystal solution between them. The crystals align as a result of an electric current, so that light cannot pass through them. Each crystal, therefore, is like a shutter, either blocking the light or allowing light to pass through.
Some of the technologies behind liquid crystal display are as follows Illumination-A cold cathode fluorescent lamp that is situated behind the LCD panel is used as an external lighting mechanism as LCD panels produce no light of their own. The conventional backlit LCDs are now being widely replaced by two types of LED backlit LCD displays. Active Matrix-This design depends on the usage of thin film transistors (TFT) — basically, tiny switching transistors and capacitors. One of the most important technologies behind liquid crystal display.
These are arranged in a matrix on a glass substrate. They are required to switch the LCD’s pixels on and off rapidly. In LCDs, each colour pixel is created by three sub-pixels with red, green and blue colour filters. Twisted Neman tics-To allow light to pass through, twisted nematic displays containing liquid crystal elements are used, these twist and untwist at varying degrees to allow light to pass though . Any grey level or transmission can be achieved by properly adjusting the level of the voltage.
Advanced fringe field switching (AFFS)-This technology provides superior performance and colour gamut with high luminosity. It helps in maintaining a wider viewing angle for a professional display and also minimizing colour distortion. Enhancement of the white/grey reproduction is achieved by optimizing the white gamut which also corrects the colour shift and deviation caused by light leakage. Vertical alignment (VA)-In this technology the need for extra transistors is removed because the liquid crystal material naturally exists in a vertical state.
When no voltage is applied a black display is created and a white display is created when voltage is applied. This is one of the most widely used technologies behind liquid crystal display Bluephase Mode-It is used to obtain a better display of moving images; it also helps in improving the temporal response of liquid crystal displays. This technology removes the usage of expensive colour filters also short switching times can be achieved so realization of time sequential colour coding can be done
Quality Control-There maybe occurrence of defective transistors in LCD panels which cause permanently lit or unlit pixels which are known as stuck pixels or dead pixels respectively. The presence of few defective transistors does not hamper the stability of the LCD panels. However the location of the defective pixels is important . it may be rendered useless if the defective pixels are clustered or are in the centre of the viewing area . also uneven patches may occur which is termed as clauding.