Liquid Crystal
Liquid Crystal, a substance that has certain properties of both liquids and solids. Like a liquid, it can flow; like a crystalline solid, it has a molecular arrangement that is symmetrical and regular. This arrangement—and thus the external appearance of the substance—can be altered readily by heat, pressure, or electricity.
Liquid crystals whose color is affected by temperature are used as heat detectors in medicine and industry. When painted on the skin, for example, they show the location of abnormally warm spots, which, in turn, may indicate the presence of tumors.
The most common use of liquid crystals is for displaying information in various kinds of electronic devices. In a typical liquid crystal display (LCD), the liquid crystal forms a layer between two clear glass plates. A thin, transparent coating of metal on each plate forms an array of electrodes. When two facing electrodes are charged, they cause the area between them to darken by changing the alignment of the adjacent molecules of the liquid crystal.
LCD's do not produce their own light. In some types, a mirrored surface reflects light that passes through the front of the display; in others, there is a source of light behind the display. In LCD's for displaying numerals in electronic calculators and watches, the electrodes are usually made in groups of seven segments arranged so that each group can display any digit. (For a picture of the type of arrangement used, More complex arrays are used in the LCD's that form the viewing screen of certain portable computers and television receivers.