| Definition: | quotient of that part of the illuminance at a point on a given plane in an interior, which is received directly from external reflecting surfaces illuminated directly or indirectly by a sky of assumed or known luminance distribution and the illuminance on a horizontal plane due to an unobstructed hemisphere of this sky, where the contribution of direct sunlight to both illuminances is excluded Note 1 to entry: When calculating the lighting of interiors, the contribution of direct sunlight has to be considered separately. Note 2 to entry: The externally reflected component of daylight factor has unit one. Note 3 to entry: This entry was numbered 845-09-99 in IEC 60050-845:1987.
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