PURPOSE:To measure the illuminance corresponding to the actual way to look of a face by providing light blocking plates, which has a shape of a width (r) or more and a height 3h or more in the direction vertical from the center of a cylinder and subjected to black non-reflecting surface treatment on the side of a light receiving window, to both side ends of the light receiving window. CONSTITUTION:The cylinder 20 of a light detection part has a radius (r) and a height H, and a light receiving window 21 is formed so as to have a radius (r) and a height (h). In order to block the light incident in a direction of a horizontal angle phi=120 deg. or more, light blocking plates 22 subjected to black non-reflecting surface treatment on the side of the light receiving window 21 are provided in the direction vertical from the center of the cylinder 20. The width (d) of each of the light blocking plates 22 is represented by d=r(1/sin30-1) when the radius of the light receiving window is (r) and the light blocking angle thereof is phi. The height h' of the light blocking plate 22 is set to three times the height (h) of the light receiving window 21 and the light blocking plates are arranged so as to become symmetric up and down around the center of the light receiving window. By this constitution, light incident at a hori zontal angle phi=90 deg. is not affected at all by the light blocking plates 22 and light incident at a horizontal angle phi=120 deg. is entirely blocked not to reach the light receiv ing window 21.
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