Daylight Factor
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5. Daylight factor

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)

Figure 6 Components of the Daylight Factor