Patent ID: 8159632

Claim:
An edge-light type surface light source element, comprising: a light-guiding plate including at least a side surface, an exit surface, and a bottom surface opposite to the exit surface, at least one primary light source disposed on the side surface of the light-guiding plate, the light-guiding plate including an incident end surface configured to enter light emitted from the primary light source, reflection means provided on a bottom surface side of the light-guiding plate and configured to reflect light, and a supporting frame to support a liquid crystal panel and an optical sheet, which are provided on an exit surface side of the light-guiding plate, if a normal line of an X-Y plane formed an X axis and a Y axis perpendicular to the X axis is a Z axis, the primary light source being disposed parallel with the X axis, the reflection means, the light-guiding plate, the optical sheet, and the liquid crystal panel supporting frame being disposed parallel with the X-Y plane, the reflection means, the light-guiding plate, the optical sheet, and the supporting frame being sequentially disposed in a direction of the Z axis, the incident end surface of the light-guiding plate being disposed parallel with an X-Z plane, a pattern formed by a plurality of concave stripes arranged parallel with the X axis being provided in the bottom surface, inclined surfaces being provided on an incident end surface side of the plurality of concave stripes and arranged parallel with the X axis, an angularity of each of the inclined surfaces to the bottom surface being substantially within a range of 25° or more to 45° or less, if an angle formed by the Z axis and a straight line which combines an intersection point of a side parallel with the X axis, of an opening boundary inside the supporting frame and a Y-Z plane and a point at which the pattern provided on the bottom surface to be parallel with the X axis and formed by the plurality of concave stripes is set first is θ, and a distance getting from the opening boundary of the supporting frame of the liquid crystal panel into a back surface of the supporting frame is L, the pattern provided on the bottom surface and formed by the concave stripes parallel with the X axis being disposed to satisfy the following equation, and the angle θ being within a range of 20° to 60°. L=T ·tan θ T: thickness of light-guiding plate (mm) L: distance getting from opening boundary of supporting frame of liquid crystal panel into back surface of supporting frame (mm).