| 摘要 |
A Fresnel lens (40) includes an incident surface (42) that is flat, and a prism-forming surface (46) that has a plurality of prisms (50), the prism-forming surface (46) being provided on the side of the Fresnel lens (40) opposite to the incident surface (42). Each of the prisms (50) has a converging surface (54) that is located on the side away from the optical axis (A) of the Fresnel lens (40). When the distance away from the optical axis (A) in the radial direction of the Fresnel lens (40) is defined as r, and predetermined values R1, R2, and R3 in the radial direction are set so as to satisfy R1<R2<R3, in a region that satisfies 0‰¤r‰¤R2, light (RL) that passes through the interior of the Fresnel lens (40) is refracted at the converging surface (54), and in a region that satisfies R2<r‰¤R3, the light (RL) is reflected at the converging surface (54). In the range of 0‰¤r<R, the relationship ¸ 2 =f(r) holds, and in the range of R1‰¤r<R2, the relationship f(R1)‰¤¸ 2 <f(r) holds, where ¸ 2 represents the angle formed between the incident surface (42) and the converging surface (54), and f(x) represents a monotonically increasing function with x as a variable. |
