Liquid crystal display device is commonly known as LCD. It is a liquid crystalline material squeezed in between two glass or plastic plates. The front plate contains coating of this film and is transparent and conductive. The back plate is reflective. Its segments are in the shape of desired characters. On the back plate an electrically conductive film is put and a voltage is applied between a segment for the back plate to create electric field in the region under the segment. The electric field makes a change in the transmission of light through the region under the segment.LCDs are available of two types: Dynamic scattering type and field effect type.
In dynamic scattering type, the molecules are aligned in one direction under the segment where field is present. In this condition, the crystalline molecules reflect more light and produces etched-glass-looking like characters on a dark background.
In field effect type, molecules are polarized to absorb light where electric field is present produces dark characters on a silver-gray background. LCDs do not emit their own light so a light source is to be used. LCDs simply change the reflection of available light. Today most LCDs used produces dark images on a silver background. The color displays have also been developed but monochrome and color displays are expected to grow rapidly in future.
In case of LCD, DC voltage is not used as it damages them. A square wave signal of 30-15Hz frequency is used and 2-3V is required between the back plate and segment
Today screen types LCDs have also developed where the crystal elements are arranged in a large x-y matrix of dots. However, these types of displays have a problem of a low resolution. LCDs are light weight and consume a little power which makes them attractive for portable computers. So, LCDs are in greatest use today.
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