A light-guide plate includes a base plate, first protrusion patterns and second protrusion patterns. The first protrusion patterns are formed on a left portion of an upper surface of the base plate with respect to a central line of the upper surface. The first protrusion patterns have a cross-section of a trapezoidal shape which has a top and a bottom parallel with each other and first and second inclined sides inclined at different angles with respect to the bottom side. The second protrusion patterns are formed on a right portion of the upper surface with respect to the central line. A cross-section of the second protrusion patterns have the trapezoidal shape and disposed substantially symmetrical to the first protrusion patterns with respect to the central line.