Patent ID: 8678635
Filing Date: 2014-03-25
Classification: G02B

Abstract:
1. A surface light source device having a light emitting surface, comprising: a light guide plate having a light exit surface and a pair of side surfaces which oppose to each other in a first direction, at least one of the pair of side surfaces serving as a light entrance surface, wherein an angular distribution of luminance of the light emitting surface in a plane parallel to both a front direction and the first direction satisfies the following relationship: where: θa is a peak angle having a maximum luminance in the angular distribution of luminance of the light emitting surface at a first end position on one side of the light emitting surface in the first direction; θb is a peak angle having a maximum luminance in the angular distribution of luminance of the light emitting surface at a second end position on the other side of the light emitting surface in the first direction; θc is a peak angle having a maximum luminance in the angular distribution of luminance of the light emitting surface at a center position of the light emitting surface in the first direction; where the front direction is defined as 0°, an angle between the front direction and a direction inclined from the front direction toward one side in the first direction is defined as negative value, and an angle between the front direction and a direction inclined from the front direction toward the other side in the first direction is defined as a positive value.