User evaluations of fabric shades with sun in the field of view: Glare model performance and implications for EN14501 Classification

Discomfort glare from daylight is common in workspaces, where daylight and luminance contrast between light
source and background can be excessive. Fabric shadings can mitigate glare, but their light transmission prop-
erties remain difficult to characterize. This study evaluates the recommended glare classes in EN17037+A1:2022
and EN14501:2021 by analyzing data from two laboratory studies (Switzerland and Argentina) and a simulation
study. The experiments involved 55 participants across 191 sessions, testing four fabrics with a low openness
factor (OF<7%). Using the Osterhaus-Bailey subjective scale for glare perception, we found comfortable glare
conditions (i.e., not disturbing nor intolerable) for 87-96% participants with class 3 and class 1 fabrics under the
tested scenarios. However, we also found that the existing tabular classification tends to overestimate glare for
fabrics with normal-normal transmittance τ$_{v, n-n}$ larger than 0.03 are involved, as well for fabrics with lighter
colors that have higher diffuse transmittances (τ$_{v, n-dif}$ >0.03). Common glare metrics (DGP, CGI, UGP) showed
strong correlations with subjective responses on the Osterhaus-Bailey scale (Spearman ρ > 0.5). ... mehrDGP showed the
highest correlation (ρ = 0.57) with a disturbing glare threshold of 0.43, indicating that the standard threshold of
0.40 slightly overestimates glare for shading fabrics when the sun is in the field of view. DGP$_{mod}$ did not perform
significantly different than DGP. ROC analysis based on binary classification confirmed acceptable to excellent
discrimination ability for DGP, CGI and UGP. Based on these findings and annual simulations, we recommend
adjustments to the glare classification in EN14501:2021.