Patent ID: 7446828

Claim:
An optical guide comprising: a first principal surface that has an effective light emitting region of substantially rectangular shape surrounded by first through fourth sides, the first side being longer than the second side; and a second principal surface that opposes the first principal surface, wherein a circumferential side face of the optical guide includes first through fourth side faces disposed along the first through fourth sides, respectively, and a light introducing section, disposed at the corner interposed between the first and second side faces, with an angle of inclination from the first side face that is determined so that center axis of light distribution intersects one of the first through fourth sides and divides the area of the effective light emitting region into two equal parts, and the light introducing section has notches comprising a first light diffusion surface that directs an incident light in a direction of the first side and a second light diffusion surface that directs an incident light in a direction of the second side, where angle Θ 1 between a reference plane perpendicular to the center axis of light distribution and the first light diffusion surface and angle Θ 2 between the reference plane and the second light diffusion surface are different so that an area of the first light diffusion surface is larger than an area of the second light diffusion surface.