| 摘要 |
PROBLEM TO BE SOLVED: To solve the problem that illuminating light tends to become nonuniform and low luminance when an image display element is illuminated by illuminating light from a light source. SOLUTION: In an image display system which irradiates an image display element 5 with illuminating light from a light source 1 through a prism sheet 18, the prism sheet is made into a sheet in which a prism column is formed on the surface opposite to the light source. When the expressed value in terms of air of an optical path length from the prism sheet to the image display element is s, and the incident angle of the illuminating light to the prism sheet isθ, the apical angle of the prism column isα, the emergent angle of the illuminating light from the prism sheet isθ', the refractive index of the prism sheet is np and the length of the side of the image display element is L,|s.tanθ'|<1.75 L/2 are satisfied toθof 40 degrees or more to 50 degrees or less, whereinθ'≡Δ-sin-1[np.sinΔ-sin-1(sinθ/np)}], andΔ≡π/2-α/2.
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