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Liquid Crystal Displays
This kind of displays rely on the special criteria of a group of chemicals, the so called Liquid Crystals (L.C.). The
Liquid Crystals are transparent and their molecules are twisted. The twist of the molecules transforms the
polarization of passing light. LCD's also re-align when subjected to an electric field. The benefits of these
characteristics have been reaped to develop displays that use the crystals to control the amount of light that is
passed through  the display. Light is produced by a backlight and is passed through a polarizing filter.When no field is applied to the LCD, the polarization of the light is changed by passing through the LC material. The light then meets a second polarizing filter that is at right angles to the first and the light is transmitted. If a field is applied to the crystal, the angle of twist changes, and only a proportion of light is transmitted. In this way the brightness can be adjusted to get the grey scale necessary for high quality images. The screen is divided up into picture elements. The image is built up by making use of these pixels. In a colour LCD, each pixel is fitted with either a red, green of blue filter. The image is made up of a matrix of pixels. The way the brightness is controlled in each individual pixel, known as the addressing, is a key difference between two types of  LCD. Those two are named  Active and Passive Matrix LCD's.
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