| 摘要 |
PURPOSE: To prevent the formation of a bright and dark pattern by superposition of prism sheets without impairing the front surface luminance as a back light by constituting lens faces of plural parallel prism arrays which vary in height. CONSTITUTION: This prism sheet 2 is constituted by parallel forming the many prism arrays 7 on one surface of a transparent sheet. The lens faces are constituted by arranging the plural prism arrays 7 varying in the height H. The plural prism arrays 7 varying in the height H include the prism arrays 7 adjusted in the height H by setting a pitch (p) constant and changing a prism vertexθ, the prism arrays 7 adjusted in the height H by setting the prism vertexθconstant and changing the pitch (p). In such a case, the pitch (p) of the prism arrays 7 is preferably selected in a range of 30μm to 0.5mm and the prism vertexθin a range of 60 to 150 deg.. As a result, the formation of bright and dark patterns by the differences in the optical paths of the wave fronts of the main rays past the adjacent prism arrays is suppressed.
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