Patent ID: 7722240
Filing Date: 2010-05-25
Classification: G02B,G02F

Abstract:
1. A surface light source device for illuminating a transmission device portion from the back side, comprising: a light source portion having an output light face for outputting substantially perfectly diffused light, a light emitting portion for emitting light, and a perfect diffusing sheet, which is adapted to provide substantially perfect diffusion of light emitted from the light emitting portion and constitutes the output light face, wherein a total light transmitivity of the perfect diffusing sheet is within a range of 50% to 70%; a light controlling sheet provided on the output light side relative to the light source portion and including unit optical structures each adapted to condense and/or diffuse light outputted from the light source portion; and a light diffusing sheet provided on the output light side relative to the light controlling sheet and including micro-convex structures formed on the output light side, the light diffusing sheet including a base layer and a light diffusing layer provided on the base layer, the light diffusing layer including multiple micro-beads and a binder for binding the micro-beads, wherein portions in which the micro-beads are bound project toward the output light side relative to the portions in which the micro-beads are not fixed and only the binder is included, thereby forming the micro-convex structures, and wherein a haze value of the light diffusing sheet is 70% or higher; wherein when aV is a half-maximum angle of light to be outputted from the light controlling sheet when the perfectly diffused light enters the light controlling sheet and is a vertical half-maximum angle that is a half-maximum angle as measured in the upward and downward directions in a normally used state of the surface light source device, and when aH is a half-maximum angle of light to be outputted from the light controlling sheet when the perfectly diffused light enters the light controlling sheet and as a horizontal half-maximum angle that is a half-maximum angle as measured in the leftward and rightward directions in a normally used state of the surface light source device, a relationship of 90°<aV+aH<115° is satisfied.