Liquid crystal display
From Sega Retro
A liquid crystal display, or LCD, is a thin, lightweight display device with no moving parts. It consists of an electrically-controlled light-polarising liquid trapped in cells between two transparent polarising sheets. The polarising axes of the two sheets are aligned perpendicular to each other. Each cell is supplied with electrical contacts that allow an electric field to be applied to the liquid inside.
Before an electric field is applied, the long, thin molecules in the liquid are in a relaxed state. Ridges in the top and bottom sheet encourage polarisation of the molecules parallel to the light polarisation direction of the sheets. Between the sheets, the polarisation of the molecules twists naturally between the two perpendicular extremes. Light is polarised by one sheet, rotated through the smooth twisting of the crystal molecules, then passes through the second sheet. The whole assembly looks nearly transparent. A slight darkening will be evident because of light losses in the original polarising sheet.
When an electric field is applied, the molecules in the liquid align themselves with the field, inhibiting rotation of the polarised light. As the light hits the polarising sheet perpendicular to the direction of polarisation, all the light is absorbed and the cell appears dark.
Uses of LCDs