Surface light source element and image display including the same

An edge-light type surface light source element, comprising:

• a light-guiding plate including a side surface having at least one primary light source, an exit surface, a bottom surface opposite to the exit surface, and an incident end surface from which light emitted from the primary light source provided in the side surface enters;
• a reflector provided on the bottom surface side of the light guiding plate, and configured to reflect light;
• and
• one optical sheet or a plurality of optical sheets provided on the exit surface side of the light-guiding plate, wherein
• if a normal line of an X-Y plane formed by an X-axis and a Y-axis orthogonal to the X-axis is a Z-axis,
• the primary light source is arranged parallel to the X-axis,
• the reflector, the light-guiding plate and the optical sheet are arranged parallel to the X-Y plane, and
• the reflector, the light-guiding plate and the optical sheet are arranged in order in the Z-axis direction,
• the optical sheets include at least one prism sheet,
• an exit surface of a prism sheet closest to the exit surface of the light-guiding plate includes a convex stripe prism, and a longitudinal direction of the convex stripe prism is arranged parallel to the X-axis,
• the incident end surface of the light-guiding plate is parallel to the X-Z plane, the bottom surface includes a pattern having a plurality of concave stripes parallel to the X-axis, and each of the concave stripes includes an inclined surface parallel to the X-axis on the incident end surface side, and
• an angularity R of the inclined surface to the bottom surface of the light-guiding plate satisfies the following conditions,
• R≦{π/2−sin−1(0.422/nLGP)}/2
• R≧sin−1(1/nLGP)−sin−1(0.643/nLGP)
• R:
• the average angularity (radian) to the bottom surface of the light-guiding plate,
• nLGP:
• a refractive index of a base material of the light guiding plate.