| 摘要 |
PROBLEM TO BE SOLVED: To provide a Fresnel lens sheet that unnecessary rays produced near the center of the concentric lens of the sheet are decreased and production of a white spot at the screen center is avoided, by forming the lens pitch near the center of the Fresnel lens sheet larger than the lens pitch in the peripheral part. SOLUTION: The beam L1 entering the peripheral part of a Fresnel lens enters the lens at a larger incident angle than the angle of the beam entering the center of the Fresnel lens. Since the beam L1 cut by the rise face 4y of the Fresnel lens does not reach the Fresnel face 4x, the beam L1 does not transmit through the region w1. The area of the region w1 where the beam L1 does not transmit is narrower in the center part of the Fresnel lens than in the peripheral part of the lens. Namely, by forming a smaller region w1, the lens pitch in the center of the concentric Fresnel lens is made larger than the lens pitch in the peripheral part.
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