Graphical Method for Determining Interflected Daylight in Clear Climates

This report presents an extension of the daylight factor method of analysis that includes a graphical method for determining interflected light in clear climates. The interflected component of daylight, called the internal reflectance component (IRC), has been determined for overcast: skies in research performed in the United Kingdom. The technique developed by the Building Research Establishmentin the United Kingdom is based on determining an average IRC for a given room or space. Using a daylight availability model developed at SERI (1), we established a similar average IRC analysis technique for clear skies. The results of applying the SERI daylight availability model suggest that a critical element in determining the IRC under clear sky conditions is the ratio of global to diffuse(G/d) illuminance on a horizontal surface. This graphical technique for determining clear sky IRC values is expected to enhance the accuracy of daylighting system design by simplifying the format used in clear sky computation.