PURPOSE: To improve the effective transmission efficiency of a light collection part by decreasing the probability of a block of transmitted light by a nonoperation surface which is a defect of a flat plate type prism plate.
CONSTITUTION: This device consists of the light collection part equipped with a prism plate 2 having plural triangular prism parts 2a1-2an of fine size on the reverse surface of a flat plate prism and a driving part which can rotates this prism plate 2 independently, and the angle α of inactive plane of each prism part satisfies 90°<'≤θL. At the light collection part constituted by stacking plural prism plates 2, the tip parts of the nonoperation surfaces of the respective prism plates 2 are provided mutually at a specific deviation distance, which is determined preferably so that maximum transmissivity can be obtained. Then the angle α of inactive plane of the prism plates 2, preferably, satisfies 90°<α≤θL and θH≤α≤θL. Here, when θL and θH are set to the projection angle of the prism plate 2 when the altitude of the sun is high.
KOIZUMI TOMOHITO
FUJIMOTO YOSHITAKE
