A curved backlight unit is provided. The backlight unit includes a curved light guide plate having a curvature, a first light source configured to provide a first illumination light to a first surface of the curved light guide plate, an array of a plurality of different grating elements disposed on a second surface of the curved light guide plate and configured to allow the first illumination light to exit the curved light guide plate from the second surface, and a second light source configured to provide a second illumination light to a third surface facing the second surface of the curved light guide plate. The curved light guide plate includes a first area configured to allow the second illumination light to exist at a first intensity and a second area configured to allow the second illumination light to exist at a second intensity that is less than the first intensity.