what's the purpose of a backlight
A backlight is a form of illumination used in liquid crystal displays (LCDs). As LCDs do not produce light themselves (unlike for example Cathode ray tube (CRT) displays), they need illumination (ambient light or a special light source) to produce a visible image. Backlights illuminate the LCD from the side or back of the display panel, unlike frontlights, which are placed in front of the LCD.