| 摘要 |
PROBLEM TO BE SOLVED: To provide an optical element which can secure a sufficient light volume while maintaining small size and is easy to manufacture and inexpensive, and to provide an auxiliary light source unit.SOLUTION: When a diagonal length of a light-emitting surface (upper surface 12a) of an LED light source 12 is denoted by S (mm), a distance from the light-emitting surface of the LED light source 12 to the farthest point (here, to the most top edge of partial circular bands RPx, RPy) of the light-emitting surface of an optical element 13 is denoted by T (mm), the largest diameter of a light transmission part 13b is denoted by L1 (mm), and the largest diameter out of diameters of the circular bands whose circumferences pass only a fan-shaped section consisting of the partial circular bands and boundaries, when drawing circles on a virtual plane in a case the optical element is projected on the virtual plane having the optical axis OA of the optical element as its normal line, is denoted by L2 (mm), following conditional expressions are satisfied: 1.5<L2/S<4.0 (1), S/3<T<2S (2), 0.1<L1xT/S<1.05 (3), provided T=T1+T2, where T1 denotes a thickness (mm) from the light-emitting surface of the LED light source 12 to the incident surface of the optical element 13, and T2 denotes a thickness (mm) of the optical element 13 in optical axis direction. |
