| 摘要 |
A lens includes a lens portion having two opposite oblong surfaces at least one of which is a curved lens surface having a reflective power. A cross-sectional area of the lens portion varies from a center toward each end in a longitudinal direction of the lens portion. A rib portion is disposed at each of two opposite sides of the lens portion adjacent to longer sides of the oblong surfaces of the lens portion, and extends along the longitudinal direction of the lens portion. A cross-sectional area of the rib portion varies along the longitudinal direction in a manner that renders variations of a cross-sectional area of a portion including the lens portion and the rib portion along the longitudinal direction of the lens portion smaller.
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