Christian Knoflach

Proper design of daylighting and electric lighting is of high relevance during the design of a building, affecting both, energy consumption and people’s well-being and health. To be able to assess the impact of different solutions, planners use simulation tools to evaluate the relevant performance indicators. Two reference simulation models are presented – one group office and one factory hall – that are used to describe and compare various lighting simulation tools, including widely used professional software as well as new research tools. Both models are set up including the required information for integrated daylighting and electric lighting simulation and include full spectral characteristics to also allow evaluating non-visual effects. Background information and a detailed description of the models are provided, and example simulation results are presented. The models provide researchers and professionals a means to test simulation tools and investigate their applicability for specific projects.

The Daylight Glare Probability (DGP) includes the luminance of a glare source quadratically, but the solid angle only linearly. While this is in line with formulae of other glare metrics, it must be questioned for small glare sources, if the glare stimulus can no longer be distinguished from larger stimuli causing equal vertical illuminance at the eye, especially in the peripheral visual field. To account for this, the modified version Daylight Glare Metric (DGM) was previously developed. We conducted two studies to evaluate the effect of the modified DGM. First, in a laboratory study under an artificial sky with an LED sun, 35 test subjects evaluated different glare situations. Second, we performed a comprehensive simulation study for an office space, including three locations, three view directions, and 17 window systems (electrochromic glazing, fabric shades). The results from the perception study under the artificial sky provide evidence that the adapted DGM is better suited to predict glare from small, bright sources. The results from the simulation study for a realistic office setting show that, compared to the DGP, the DGM reduces glare ratings for many hours of the year, thus underscoring the practical relevance of improving the DGP formula.

EN 17037 defines essential properties of daylight in buildings: daylight provision, view out, sunlight exposure and glare protection. For assessing glare, the standard proposes the daylight glare probability (DGP) metric. A look at the formula reveals the following problem: since the luminance is included quadratically, but the solid angle only linearly, small but bright glare sources (e.g. the sun) are rated highly. This must be questioned if the glare stimulus can no longer be distinguished from larger stimuli causing equal vertical illuminance at the eye, especially in the peripheral visual field. For the unified glare rating for artificial lighting, this is avoided by limiting the minimum solid angle of the glare source. There is nothing comparable for the DGP. We present a simulation study on how the DGP changes with the bidirectional scattering distribution function resolution for complex fenestration systems or with rendering the sun at its real size. We performed subject experiments on the discriminability of small light stimuli in the periphery in a laboratory setup. Based on the findings, we propose adjusting the DGP by limiting the minimum glare source solid angle depending on its position in the field of view. We conclude with an evaluation of the simulation results with the modified metric daylight glare metric (DGM) and point out open issues that still need to be investigated.