Analysis and evaluation of BSDF characterization of daylighting systems

This technical report summarizes the current state of the art in the field of characterization of daylighting and shading systems by bidirectional scattering distribution functions (BSDFs) and documents the results of an inter-laboratory round robin test. It is the result of collaborative work conducted by members of the IEA SHC Task 61 / EBC Annex 77, Subtask C2. In the first part, various methods for generating BSDF data sets for shading and daylighting systems as applied by different laboratories are documented and compared. Worldwide, several institutes provide the service of measuring and simulating BSDF data for such fenestration systems. However, the labs use various measurement devices as well as different generation workflows with their respective advantages and disadvantages. At the same time, different daylight simulation tools require different BSDF data formats for importing daylighting and shading systems into the software. The aim here is to highlight the pros and cons of the different approaches and to provide an overview of used measurement instruments and simulation software tools. In the second part, a round robin test performed among the project participants is documented. The objective was to assess the comparability of BSDF data sets generated by various laboratories for the same shading or daylighting system as well as – for practical use in daylighting design even more important – the comparability of daylight performance metric evaluations based on these data. One outdoor venetian blind system and one interior textile roller blind were selected representing widely used shading and glare protection systems. The contributing laboratories generated BSDF data sets for samples of these two systems according to their usual routine. The data sets were analyzed and applied in daylighting simulations to evaluate point-in-time and annual daylight performance metrics. The overall result of the comparison sho