Modelling indoor illumination by complex fenestration systems based on bidirectional photometric data

Significant efforts to assess the bidirectional transmittance distribution functions (BTDFs) of complex fenestration systems (CFS) have been undertaken in recent years. This paper presents a methodology for including these photometric raw data sets into the daylighting simulation and design process. The method is based on computing the luminous intensity distribution on the inward facing side of façade elements from BTDF data (measured or calculated) and the outside luminance distribution as seen from the façade element. Fourier optical principles are applied to derive filter conditions for BTDF interpolation. Since the BTDF raw data sets are big in volume, data compression techniques are introduced and applied. Control algorithms for dynamic façade systems (i.e. time variant systems like automated blinds) are accounted for. The procedure is validated against analytical and numerical test cases. Limitations of the approach are being discussed. As an application example, the method is incorporated into lighting simulation engines and into a complex fenestration system database.