Patent ID: 7497610

Claim:
A light guiding plate comprising: a pair of main surfaces opposite to each other; and an end surface on which light emitted from a light source is incident, wherein one of the pair of main surfaces has a plurality of prisms, and the light from the light source incident from the end surface propagates through the inside of the light guiding plate and exits from the prism, each of the prisms having a first surface which is disposed near the end surface and has a relatively gentle slope, a second surface which is disposed more distant from the end surface than the first surface and has a relatively steep slope, and a third surface located between the first surface and the second surface, wherein an angle between the second surface and the third surface is an acute angle, wherein the first surface is configured to reflect light from the end surface such that the light is propagated between the pair of main surfaces, and wherein the second surface is configured to reflect light from the end surface to the third surface such that the light is transmitted through the third surface, thereby passing outside the light guiding plate, wherein the third surface is substantially parallel to a horizontal reference plane and wherein an angle between the first surface and the horizontal reference plane is an acute angle θ 1 in a light propagating direction and an angle between the second surface and the horizontal reference plane is an acute angle θ 2 in the light propagating direction where θ 2 >θ 1 , wherein the angle between the second surface and the third surface is set such that light incident from the end surface is reflected from the second surface and then the reflected light exits outside from the third surface, and wherein a length of the third surface is equal to or smaller than a length when the second surface is projected onto the third surface.