Development of protractors for calculating the effects of daylight from clear skies

A procedure Is described for calculating Interior daylight Illumination from clear skies using a protractor approach. The proposed procedure closely parallels the one used by the British Building Research Station In preparing daylight protractors for calculating daylight from overcast skies. Building on this work, a computer program was developed which used the CIE clear sky function to execute the numerous calculations needed to construct the clear sky protractors. The proposed procedure was validated against the Qulckllte I daylighting program, the results of which suggest a close correlation between the Protractor procedure and Qulckllte I. Thus, an accurate, simple and relatively fast procedure for calculating daylight has been presented which enables measurements to be made directly from architectural drawings.