LCD display screens use a gridwork of cells which contain a special liquid ~polymer~. The cells are sandwiched between two sets of electrodes which are used to energize the individual pixels. In the front of the display, a laminated, ~polarizing filter~, darkens a pixel if the cell is turned on. The whole display usually is protected by a plastic or glass shell.
Many systems use ambient light through use of a mirror behind the display. This is both easy and inexpensive to make. Others, called "backlit", provide their own light from a panel behind the LCD cells. An ~electroluminescent panel~ commonly is used for this.
