To provide a lens sheet which is excellent in the control of the diffusion angle of existing light rays from a light source and is superior in the availability of the existing light rays in order to obtain high luminance, an optimum viewing angle, a high contrast or the like, and to provide an optical sheet and a back light with the optical sheet.

In the lens array sheet, which has a lens surface where a plurality of convex unit lenses are arrayed in two dimensions at a predetermined pitch and a flat surface on the opposite side from the lens surface, a light reflective layer reflecting a light beam to a light non-convergence surface region of the lens is formed on the flat surface.

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