A backlight unit comprising: a light guide plate including at least one first region having a light incident surface and a second region; and a light source assembly including a plurality of light sources disposed adjacent the light incident surface of the first region and arranged to provide incident light through the light incident surface, wherein the second region extends away from the first region in a direction in which incident light from the light source assembly is arranged to travel; wherein the first region includes a plurality of first patterns and the second region includes a plurality of second patterns, wherein the plurality of first patterns and the plurality of second patterns are depressed engraved patterns and the first patterns have a depth deeper than a depth of the second patterns; wherein the plurality of light sources are arranged in a first direction, and wherein the plurality of second patterns are arranged such that light incident from the light sources is irregularly reflected by the plurality of second patterns to convert the light from the light sources into a plane light source, and characterized in that the plurality of first patterns comprises a closed portion in the first direction, an open portion in the first direction and side surfaces to form an open trapezoidal shape in a plan view, wherein the closed portion is shorter than the open portion and the closed portion is positioned closer to the light sources than the open portion, the plurality of first patterns being adapted to diffuse light incident from the plurality of light sources over a wider area in the light guide. a light guide plate including at least one first region having a light incident surface and a second region; and a light source assembly including a plurality of light sources disposed adjacent the light incident surface of the first region and arranged to provide incident light through the light incident surface, wherein the second region extends away from the first region in a direction in which incident light from the light source assembly is arranged to travel; wherein the first region includes a plurality of first patterns and the second region includes a plurality of second patterns, wherein the plurality of first patterns and the plurality of second patterns are depressed engraved patterns and the first patterns have a depth deeper than a depth of the second patterns; wherein the plurality of light sources are arranged in a first direction, and wherein the plurality of second patterns are arranged such that light incident from the light sources is irregularly reflected by the plurality of second patterns to convert the light from the light sources into a plane light source, and characterized in that the plurality of first patterns comprises a closed portion in the first direction, an open portion in the first direction and side surfaces to form an open trapezoidal shape in a plan view, wherein the closed portion is shorter than the open portion and the closed portion is positioned closer to the light sources than the open portion, the plurality of first patterns being adapted to diffuse light incident from the plurality of light sources over a wider area in the light guide.