Graphical Method for Determining Interflected Daylight in Clear Climates

    Research output: NRELTechnical Report


    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.
    Original languageAmerican English
    Number of pages8
    StatePublished - 1983

    NREL Publication Number

    • NREL/TP-254-2027


    • daylight factor
    • interflected light
    • internal reflectance component


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