An optical plate includes a first surface and a second surface opposite to the first surface. A plurality of elongated, arc-shaped depressions is defined in the first surface. A plurality of elongated, arc-shaped protrusions and a plurality of elongated, V-shaped protrusions protrude from the second surface. An extending direction of the elongated, arc-shaped protrusions intersects with an extending direction of the elongated, V-shaped protrusions. An extending direction of elongated, arc-shaped depressions is substantially parallel with the extending direction of the elongated, arc-shaped protrusions.