This algorithm gives the sky component (from a CIE overcast sky) on a horizontal plane due to an unglazed vertical rectangular opening which has its lower edge in the reference plane and one vertical edge in a plane perpendicular to the opening and containing the reference point.

*Input*- Angles
*a*,*b*and*c*from figure above*radians* *Equation**Note*- When the opening is
*H*high,*W*wide and a perpendicular distance*D*away from the reference point,

- To obtain the sky component for a opening with clear 6mm glass, the value
*Ds*obtained from this algorithm may be multiplied by the transmittance*T*obtained from algorithm 2.34. *Source*- Walsh(1)
**References**- 1. Walsh J W T
*The science of daylight*(London: Macdonald) (1961)

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