Complex fenestration systems (CFS) need to be evaluated to quantify how well they contribute to avoid glare and manage the solar heat gains through building façades. It is possible to use solar bidirectional properties of CFS in some building energy simulations tools in order to evaluate more accurately their impact on lighting, cooling and heating energy consumption. genBSDF is a Radiance’s program whose capabilities of assessing the bidirectional solar properties of CFS are evaluated in this paper. This evaluation was carried out for 16 cases of a venetian blind varying the solar properties and slope angle of the slats. Results of directional and bidirectional solar properties obtained by genBSDF with radiosity assumptions were compared with the results of the radiosity-based WINDOW algorithm. Results show an excellent agreement between the two approaches which demonstrates that genBSDF is a very precise and robust tool for assessing the solar bidirectional properties of CFS.