The daylight factor is defined as
:
(3)
where
Ei =
illumiance due to daylight at a point on the indoors working plane
Eo =
simultaneous outdoor illuminance on a horizontal plane from an unobstructed hemisphere of
overcast sky
There are three possible paths
along which light can reach a point inside a room through glazed windows (See Figure 6).
They are :
(a) light from the patch of sky
visible at the point considered, expressed as the sky component (SC),
(b) light reflected from opposing
exterior surfaces and then reached the point, expressed as the externally reflected
component (ERC),
(c) light entering through the
window but reaching the point only after reflection from internal surfaces, expressed as
the internally reflected component (IRC).
The sum of the three components
gives the daylight factor:
(4)