Accurate determination of the luminous and thermalsperformance of fenestration systems that incorporatesoptically complex components requires detailedsknowledge of their radiant behavior. We describe a largesscanning radiometer used to measure the bidirectionalstransmittance and reflectance of fenestration systems andscomponents. We present examples of measured datasobtained for simple non-specular samples. We describesa method of obtaining the overall properties ofsfenestration systems by calculation from scanningsradiometer measurements of fenestration components.sFinally, we describe the application of bidirectionalssolar-optical properties of fenestration systems tosdetermine their luminous and thermal performance withsrespect to building energy consumption and occupantsscomfort. We also discuss the advantages and limitationssof the method, which appears to be promising.