The degradation of directivity performance due to stray light with poor directivity entering and propagating through tapered light guiding members can be prevented, and thus the decrease in the degree of spectrum correspondence with sunlight can be prevented. A light shielding member 41 is placed in between adjacent tapered light guiding members 4. Specifically, the light shielding member 41 is attached to or coiled around the surface of a circumference wall of the tapered light guiding member 4, other than one end surface and the other end surface for allowing light to enter and exit. Further, the light shielding member 41 is placed so that stray light will not enter the tapered light guiding member 4 from the circumferential wall thereof, other than the one end surface and the other end surface.
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