A backlight system (300) includes a light guide plate (3024), a reflection plate (3023), a light source (3021) disposed at one side of the light guide plate, a diffusion plate (3025) and a reflection polarizer (3027), which allows light polarized in one certain direction to pass, and reflects light polarized in a direction perpendicular to said one certain direction. The diffusion plate, the light guide plate, the diffusion plate, and the reflection polarizer are stacked up one on top of the other. A plurality of prisms (11) are disposed on a surface of the diffusion plate, thereby defining a plurality of V-shaped grooves (not labeled).