Some liquid crystal displays have a light source behind the LCD cells. These are known as "backlit" displays. These are commonly ~electroluminescent~, where the light source is a layer of phosphor sandwiched between two electrode plates. The plate facing the screen is transparent, allowing the light to pass through. It is this light which is ~polarized~ by the LCD cells and blocked by the ~polarizing filter~ to darken the pixels. Displays that aren't backlit use a mirror to reflect ambient light through the screen. This is much less expensive, but cannot be used in low light situations.
