Sky Component/Vertical Sky Component

The ratio of the illuminance at a point on a given plane within an interior due to the light received directly 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).
Note: this is the same as the Daylight Factor except the indirect component has been removed.
E = illuminance on unobstructed plane
e = illuminance at point in interior
              Sky Component = e/E (often expressed as a percentage)
              Vertical Sky Component = v/E