| Definition: | ratio of the illuminance at a point on a given plane due to the light received directly or indirectly from a sky of assumed or known luminance distribution, to the illuminance on a horizontal plane due to an unobstructed hemisphere of this sky. The contribution of direct sunlight to both illuminances is excluded
NOTE 1 – Glazing, dirt effects, etc. are included.
NOTE 2 – When calculating the lighting of interiors, the contribution of direct sunlight must be considered separately.
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