Patent ID: 7868970

Claim:
A transparent light guide plate, comprising: a rectangular light exit surface that constitutes a front portion; and back surfaces that constitute a back portion and which have a shape symmetrical with respect to a symmetry plane that includes a center of said light exit surface and which is perpendicular to one side of said light exit surface, wherein said back surfaces have such a sectional profile that when a section of said light guide plate is taken through a plane that is parallel to said one side and which is perpendicular to said light exit surface and when a point at which an end face of said light guide plate is connected to one of said back surfaces is designated an origin, a position from said origin in a direction parallel to said one side is written as X, and a position from said origin in a direction perpendicular to said one side is written as Y, said sectional shape of each of said back surfaces is expressed by part of a curve that satisfies the following 10 th -order function formula: Y=A 0 +A 1 ×X+A 2 ×X 2 +A 3 ×X 3 +A 4 ×X 4 +A 5 ×X 5 +A 6 ×X 6 +A 7 ×X 7 +A 8 ×X 8 +A 9 ×X 9 +A 10 ×X 10 −1.3×10 5 ≦A 0 ≦2.4×10 5 , −2.0×10 4 ≦A 1 ≦9.4×10 4 , −2.6×10 4 ≦A 2 ≦5.7×10 4 , −5.5×10 3 ≦A 3 ≦2.2×10 3 , −2.1×10 2 ≦A 4 ≦1.1×10 2 , −3.7×10 ≦A 5 ≦2.2×10, −1.4×10 ≦A 6 ≦3.3×10, −3.6 ≦A 7 ≦1.5, −7.8×10 −2 ≦A 8 ≦3.3×10 −2 , −1.2×10 −2 ≦A 9 ≦3.2×10 −2 , −1.4×10 −3 ≦A 10 ≦4.9×10 −4 .