'The Daylighting and Perception Research Group of the Solar Energy and Building Physics Laboratory (LESO-PB), works on advanced systems for optimal use of daylight in buildings, with the aim of improving user comfort and reducing energy consumption.   A brief overview of the Lab's capabilities and research will be given. In addition, the talk will focus on a study that compares the daylighting performance of complex fenestration systems in buildings.  Complex fenestration systems are widely studied to help redirecting daylight into a room in order to optimise its luminous properties. Daylighting designers and researchers usually use physical and virtual models to assess daylighting performance within buildings. However, these models do not necessarily provide for a perfect analysis of real buildings' performance due to a multiplicity of possible sources of error.  To study this, physical and virtual models of a simple building equipped with a complex fenestration system are being investigated using computer simulations of a real object (a 1 : 1 scale daylighting test module) carried out using the Radiance program, as well as monitoring of a 1:10 scale model placed under a scanning sky simulator. Sensitivity studies of different model parameters, both for simple and complex fenestration systems, are also considered.