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sky factor
quotient of the illuminance on a horizontal plane at a given point inside a building due to the light received directly from the sky and the illuminance due to an unobstructed hemisphere of sky of uniform luminance equal to that of the visible sky
Note 1 to entry: The sky factor has unit one.
Note 2 to entry: This entry was numbered 17-1190 in CIE S 017:2011.