Patent ID: 8199278
Filing Date: 2012-06-12
Classification: G02B

Abstract:
1. A surface light source device comprising: at least one light source; a light guide plate having (i) two end parts in its length direction, at least one of which serves as an incident surface, and (ii) two end parts in its thickness direction which serve as an exit surface and a back surface, the light guide plate directing light, emitted from the at least one light source, incident on the incident surface, so as to cause the light to exit from a substantially entire area of the exit surface, and at least one reflector which reflects and directs, toward the incident surface, part of the light which is emitted from the at least one light source and is then reflected from the incident surface, the incident surface having at least one concave part whose shape is identical to an elliptic arc which is a part of at least one ellipse having a first focal point which corresponds to said at least one light source and a second focal point which corresponds to said at least one reflector, and said at least one light source and said at least one reflector being respectively provided on first and second trajectory straight lines parallel to each other, the first trajectory straight line being obtained by moving the first focal point in a width direction of the light guide plate, the second trajectory straight line being obtained by moving the second focal point in the width direction, the first and second focal points being focal points of the at least one ellipse including a surface shape of the at least one concave part as its elliptic arc.