Experimental validation of simulation methods for bi-directional transmission properties at the daylighting performance level

The objective of this paper is to assess the capability of existing lighting simulation methods to predict the performance of complex fenestration systems (CFS), whose potential in daylight and sunlight control make them an increasingly popular alternative to conventional glazing. The research was conducted in two phases. First, collect reliable reference data by taking illuminance measurements inside a black box under a measured and controlled external luminance distribution, the black-box’s only aperture being covered with a complex glazing sample. Two types of materials were used: a Serraglaze element and a Laser Cut Panel (LCP). Several simulation methods were then investigated and validated against this reference case. On one hand, measured BTDF for both material samples were integrated in different simulation tools to determine the resulting indoor lighting conditions under the external luminance distribution chosen for the reference case. The same method was then applied with calculated BTDF data, based on ray-tracing calculations. Finally, one of the CFS (the LCP) was modeled in a backward ray-tracing program so that the inside illuminance distribution could be deduced without requiring BTDF data to be used. The comparison between the experimental reference data and the simulation results showed that the effect of the CFS on the room’s illumination could be predicted with acceptable accuracy for most of the tested methods (generally within 10%-20%). The simplicity of the testing scenarios allowed error sources related to simulation to be highlighted and helped determine the extent to which an accurate physical description of the samples could influence the results. Based on this study, recommendations were made for a better use of existing simulation methods.