Patent ID: 7845811

Claim:
A prism sheet for a direct backlight, comprising: a light input surface; a light output surface opposite to the light input surface; and a plurality of micro-depressions arranged and aligned in a skewed matrix, the skewed matrix comprising rows and columns, the rows forming a plurality of first circular arcs having a predetermined S-shaped curvature, and the columns forming a plurality of second circular arcs having a predetermined S-shaped curvature, the prism sheet defining the plurality of micro-depressions in the light output surface, wherein each micro-depression has four side surfaces connected to each other, and a transverse width of each side surface decreases along a direction away from the light output surface and close to the light input surface; each micro-depression has a shape that follows a contour defined by the rows and columns of the skewed matrix, a pair of side surfaces of each micro-depression being formed along the first circular arc and the other pair of side surfaces of each micro-depression being formed along the second circular arc; the first circular arcs are smooth, continuous, and coplanar with the light output surface, and the second circular arcs are smooth, continuous, and coplanar with the light output surface.