Daylight Factor (DF) is defined as the ratio of the illuminance at a point on a given plane within an interior due to the light received directly and indirectly from a sky of assumed or known luminance distribution, to that on a horizontal plane due to an unobstructed hemisphere of this sky. Direct sunlight is excluded from both values of illuminance (i.e. CIE Overcast Sky). Daylight Factor is normally expressed as a percentage.
Sky Component (SC) is the same as Daylight Factor except the indirect component has been removed.
Sky Factor is a variation on the Daylight Factor – the difference being instead of using the CIE Overcast Sky a Uniform Sky is used.
E = illuminance on unobstructed plane
e = illuminance at point in interior
Daylight Factor = e/E (often expressed as a percentage)
