A backlight unit that can perform local dimming, and has a structure for preventing light leakage and a cooling structure, and an image display apparatus employing the backlight unit. The backlight unit includes a light emitting arrangement adapted to radiate light and a plurality of light. shielding guides adapted to divide the light emitting arrangement into a plurality of unit blocks, the unit blocks being adapted to provide local dimming, the light shielding guides being further adapted to prevent light from traveling from one of said unit blocks to another of said unit blocks.