Liquid Crystal Display
LCD is a type of display technology used by digital watches, portable computers and video monitors.
LCD monitors are gradually replacing regular video monitors based on CRT technology. Until very recently LCD displays were found only on portable computers, but since 1997 several manufacturers started developing and selling LCD video monitors for the average user. Since them the price has dropped a lot and nowadays LCD monitors are reasonable priced.
Monochromatic LCD displays normally provided gray, blue, green any other dark color over a light gray background. Colored LCD displays can basically use two technologies: passive matrix or active matrix (a.k.a. TFT, Thin Film Transistor).
LCD has several layers: backlight, polarizer (1), liquid crystal, color filter (red, green and blue), polarizer (2) and glass.
In order to generate the image to be displayed, the backlight goes through the first polarizer, which makes the light to go in just one way. This light reaches the liquid crystal, which rotates the light in an angle of 90 degrees on the spots (pixels) where the light should pass through all the way to the screen (i.e. a pixel to be turned on). The light that was turned 90 degrees can pass the second polarizer, reaching the screen.
There are LCDs that don’t have backlight, like the ones used on calculators and watches.