How It Works

A LIQUID-CRYSTAL DISPLAY (LCD) is a sandwich containing two plates of glass with polarizing filters that are perpendicular to each other. Under normal circumstances, no light could pass through. In an LCD, however, the area between the glass plates is filled with liquid crystals, and the inner I side of each plate is grooved uanot in the direction of polarization. Under these conditions, the liquid-crystal molecules form spirals that rotate the polarization of the light, allowing it to be transmitted.

In addition, the bottom plate is covered with a layer of a transparent conducting substance. Areas meant to be blacked out (the 8 in our illustration) are covered with the same substance on the top plate. When a current is applied between one or more segments of the 8 and the bottom plate, the liquid-crystal spirals in between untwist and stop rotating the light. This makes the corresponding areas of the display appear dark. In a laptop computer screen, the same principle is used on a much finer level, allowing the display to be controlled pixel by pixel.