A liquid crystal display, or LCD, consists of a rather unique substance called liquid crystal. Most matter exists in one of three states - solid, liquid, or gas. Typically, temperature and/or pressure converts a material between these states. Liquid crystal can exist in an intermediate state between solid and liquid, within a narrow temperature range.
When liquid crystal enters the liquid crystal state, it exhibits properties common to both solids and liquids. Like a liquid, the individual molecules that make up the material are free to move around. Like a solid, the molecules can be made to hold their position. Applying electricity to liquid crystal causes its molecules to change position.
In a twisted-nemonic LCD, liquid crystal is sandwiched between two substrates, each with a polarized surface. The polarization of each surface is at a 90 degree angle with respect to each other. Normally, when two polarized surfaces are placed this way, they block the passage of light. In an LCD, the molecules of the LC sandwiched between the two surfaces twist gradually from the zero to 90 degree angle formed by the two surfaces. Light propagates along this twist, and is made to pass through the sandwich.
When a voltage is applied to the liquid crystal, the molecules respond by changing their position. They begin to "untwist," and turn lengthwise with respect to the two polarized surfaces. The greater the voltage, the greater degree of "untwisting", and light has a more and more difficult time passing through the sandwich.
A matrix or panel of these liquid crystal "cells," can be made to form moving images by varying the voltage for each according to a video input. Adding a backlight increases its brightness. Color can be achieved by using three different LC "cells" for each pixel, each with a red, green, or blue gel or screen. Or a simple monochrome, 7 cell digit with a reflective panel for backlighting can be created for much less cost.
Related Technologies
Active Matrix
TFT
Widescreen
