Many electronic devices nowadays have liquid crystal displays. Watches, music centres, calculators and even cars give information by means of liquid crystals. These are crystals, held inside cells that become opaque or change colour when they are heated. The circuits behind the display pass a voltage across the crystals, so that some of them change while the others remain the same. In this way, numbers, letters and symbols can be displayed.
Liquid crystal display (LCD), electronic display device that operates by applying a varying electric voltage to a layer of liquid crystal, thereby inducing changes in its optical properties. LCDs are commonly used for portable electronic games, as viewfinders for digital cameras and camcorders, in video projection systems, for electronic billboards, as monitors for computers, and in flat-panel televisions.
Liquid crystals are materials with a structure that is intermediate between that of liquids and crystalline solids. As in liquids, the molecules of a liquid crystal can flow past one another. As in solid crystals, however, they arrange themselves in recognizably ordered patterns. In common with solid crystals, liquid crystals can exhibit polymorphism; i.e., they can take on different structural patterns, each with unique properties. LCDs utilize either nematic or amectic liquid crystals. The molecules of nematic liquid crystals align themselves with their axes in parallel, Smectic liquid crystals, on the other hand, arrange themselves in layered sheets; within different smectic phases, the molecules may take on different alignments relative to the plane of the sheets.
The optical properties of liquid crystals depend on the direction light travels through a layer of the material. An electric field (induced by a small electric voltage) can change the orientation of molecules in a layer of liquid crystal and thus affect its optical properties. Such a process is termed an electro-optical effect, and it forms the basis for LCDs. For nematic LCDs, the change in optical properties results from orienting the molecular axes either along or perpendicular to the applied electric field, the preferred direction being determined by the details of the molecule’s chemical structure. Liquid crystal materials that align either parallel or perpendicular to an applied field can be selected to suit particular applications. The small electric voltages necessary to orient liquid crystal molecules have been a key feature of the commercial success of LCDs; other display technologies have rarely matched their low power consumption.
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