| 摘要 |
An optical element that condenses light emitted from a light source has: an entrance surface where the light enters; an exit surface from which the light entering inside via the entrance surface; and a reflection surface that directs, to the exit surface by total reflection, part of the light entering the inside via the entrance surface. The reflection surface has an axis of symmetry of sixfold or higher-order-fold rotation. The optical element fulfills conditional formula: 0.3<a/b<1.4, where a denotes the maximum length of the exit surface in the direction perpendicular to the axis of symmetry; and b denotes a surface gap on the axis of symmetry between the entrance surface and the exit surface. As a result, an optical element can be provided which achieves highly efficient condensation at low costs and with simple configuration and also which achieves compactification by reducing the diameter of the optical element for the size of the light emitting surface.
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