Patent ID: 8403550
Filing Date: 2013-03-26
Classification: G02B

Abstract:
1. A surface light source device comprising: a light guiding plate having a first end surface and a second end surface being narrower than the first end surface, a light exiting surface including a light exiting portion, and a tapered surface disposed opposite to the light exiting surface and tapered with respect to the light exiting surface from the first end surface to the second end surface of the light guiding plate; a light source disposed along the first end surface of the light guiding plate; a reflection sheet disposed along the tapered surface of the light guiding plate; and a prism sheet having a prism surface facing toward the light exiting portion of the light guiding plate, wherein the light exiting portion is disposed a predetermined entrance length L away from the first end surface along a direction perpendicular to the first end surface so that the light exiting surface within a plane perpendicular to the first end surface forms a predetermined angle with the tapered surface as a taper angle γ, wherein the taper angle γ satisfies the following equations (1) and (2), and the entrance length L satisfies the following equation (2): wherein m: the number of reflections of the light beams, incident on and substantially perpendicular to the first end surface, reflected by the tapered surface, n n β: the light exiting angle by which the light beams exit from the light exiting portion to the prism sheet (unit: degrees), a: the thickness of the light guiding plate at the first end surface, b: the thickness of the light guiding plate at the second end surface, and L