A new approach to measuring angular-dependent transmittance values of extended complex fenestration systems with a near field goniophotometer

• A near field goniophotometer was realized using an angle filter at the detector. • Comparison of near field and far field goniophotometer revealed strong agreement. • Ray tracing simulation exhibited low absolute errors for direct-direct transmission. • The simulation replicated the scattering effect of a mirror lamella. The knowledge of angle-dependent transmittance values is crucial for many areas in the built environment, such as visual and thermal comfort assessment or energy demand calculation. Measurement devices used for complex fenestration systems are typically far field goniophotometers, which require a large distance between sample and detector. As alternative to conventional far field devices, a near field goniophotometer to measure angle-dependent transmittance values of shading systems was developed. The new device is aimed at extended shading systems with structural elements, such as blind systems. This is realized by combining large-area detectors with an angle filter of a specific angular sensitivity curve. The measurement principle and prototypical setup are explained and requirements of divergence of the light source and the detector are formulated followed by a thorough discussion of the results. A comparison between near field and far field measurements was carried out. A raytracing simulation model that replicates the measurement procedure was used for comparison with measured data. All measurements were carried out with an artificial light source and fixed incidence angles in normal direction to the sample. The comparison of measured and simulated transmittance showed low absolute errors. The scattering effect of a mirror lamella found in the measurement could be replicated by the simulation. Some differences in absolute transmittance of the mirror lamella, which might be caused by effects that are not covered in the simulation model, were found between measurement and simulation. A qualitative and quantitative analysis of errors and uncertainty was carried out.