Visual comfort without borders: Extending daylight glare prediction to dim daylit environments (2018-2022)

Thesis abstract

Link to thesis:

Avoiding discomfort glare is one of the critical aspects of maintaining visual comfort, which significantly influences occupants’ overall satisfaction with their indoor environment. Discomfort glare prediction models have been developed for various lighting conditions, and their equations commonly use either contrast and/or saturation terms to account for glare caused by excessive luminance contrast or excessive overall brightness, respectively. Daylight Glare Probability (DGP), which includes both terms (hybrid model) and thus accounts for both effects, is one of the more robust ones. However, the predictive performance of discomfort glare models is limited to the luminous conditions and light source types found in the dataset from which they were developed. As daylight glare models like DGP are typically derived from glare evaluations in brightly lit environments, their performance in dimmer conditions, such as those found in deep open-plan workspaces away from the window, could be limited. This thesis, therefore, aims to extend the prediction range of existing discomfort glare models to reliably cover low-light ranges as well. To determine which conditions are most critical to focus on, the luminous ranges covered in previous laboratory studies were compared to those that can be expected in open-plan offices where low-light conditions may occur. The identified range of missing lighting conditions was then used to design and conduct two new user studies in semi-controlled dim daylit conditions to supplement prior discomfort glare datasets. In the first study, participants evaluated four scenes in which the size and luminance of the glare source were varied, and in the second, participants evaluated four scenes in which it was the size and position of the glare source were varied. In parallel, the models that currently perform best in dimmer conditions were identified using an existing dataset of glare evaluations in daylit conditions: contrast-driven models were shown to outperform saturation-driven models in dim conditions, while the more versatile hybrid metrics tended to perform well overall. Hence, the hybrid format was found to be better suited for extending glare models. To create a comprehensive training dataset for this model extension, the data obtained from the two user studies were combined with experimental data from other recent studies containing high-contrast scenarios, namely with the sun disc visible through fabric shadings and low-transmittance glazing. A new best-fit discomfort glare prediction model was then proposed for the broader targeted range of luminous conditions. Based on preliminary performance checks, the new hybrid model appears to fit the participants’ glare responses better in low-light conditions than the reference model, DGP, while maintaining a fit equivalent to DGP in brightly lit conditions. The new user studies also revealed an unexpected finding: the summation of multiple glare sources in glare model equations can sometimes result in an over-prediction of discomfort glare. More research will be needed to validate the newly proposed model using a larger test dataset that does not include data points used for any model development. This thesis’ findings may help to advance daylight glare prediction in indoor spaces by broadening the range of validity of prediction models to dimmer conditions, thus improving the overall reliability of visual comfort appraisal in the built environment.


Quek, G., Wasilewski, S., Wienold, J., & Andersen, M. (2021). Spatial evaluation of potential saturation and contrast effects of discomfort glare in an open-plan office. Building Simulation 2021 Conference.

Quek, G., Wienold, J., & Andersen, M. (2021). User evaluations of contrast-dominant discomfort glare in dim daylit scenarios: Preliminary findings. CIE 2021 Midterm Meeting & Conference. Living with Light, Kuala Lumpur, Malaysia.

Quek, G., Wienold, J., Khanie, M. S., Erell, E., Kaftan, E., Tzempelikos, A., Konstantzos, I., Christoffersen, J., Kuhn, T., & Andersen, M. (2021). Comparing performance of discomfort glare metrics in high and low adaptation levels. Building and Environment, 108335.

Project abstract

Establishing reliable and objective measures of daylight comfort remains a crucial step to moving towards optimal building design; yet despite numerous efforts in developing visual comfort models through human assessment studies, predicting visual comfort in indoor environments still poses important challenges. So far, existing visual comfort models only partially explain people´s visual comfort perception, and embed high uncertainties in their ability to anticipate the borderline between comfort and discomfort. The reasons why existing visual comfort models show high uncertainties in predicting user’s response are manifold. First of all, the models ignore the influence of the visual system (e.g., gaze reaction to the visual environment, contrast sensitivity, eye color). Second, commonly used metrics penalize a contrasted environment and neglect its positive impact on the users. Third, current glare models either concentrate on the saturation effect (e.g. DGP) or use contrast as a measure for glare (e.g. DGI, UGP): as a result, they typically perform worse when both glare-inducing factors occur simultaneously (e.g. DGP in dark and contrasted scenes or DGI in very bright low contrast scenes). And fourth, other potential influencing factors like temperature, color temperature or time of the day are not taken into account. Also, existing prediction models mostly concentrate on predicting discomfort, ignoring the positive aspects of contrasted light distributions. For example, in the same situation, a space’s occupants might perceive glare from the window, but would not describe the space as uncomfortable because they find it “exciting” or “stimulating”. As a consequence, people’s reactions remain difficult to predict with regard to the ways in which they may act upon their perception, such as through interaction with shading devices and/or with electric lighting. This often leads to an energy demand higher than anticipated, given that daylight availability in the built environment may reduce the need for complementary electric lighting and/or for heating in the winter thanks to solar gains, but only if controlled, anticipated, and managed adequately. The goal of this project continuation is to have a better, deeper, and more objective understanding of the various factors impacting glare in order to improve our ability to predict and evaluate visual comfort in spaces and ultimately to improve design tools and the planning process of buildings. The work will be structured in 3 research tracks:-Track 1 (“Contrast”) will investigate in depth the influence of contrast on glare and consider its interplay with positive contrast – it will be conducted in the laboratory and in Virtual Reality environments. -Track 2 (“Interactions”) will examine the influence of the visual system, color, temperature, and time of day – this track will be conducted only in laboratory environments.-Track 3 (“Validation and tool”) will validate the gaze model developed in the first (concluded) SNF project, as well as the findings from Track 1 and Track 2 by means of user assessments in real office spaces (POE-studies). Existing glare prediction models will be extended to account for the influencing factors that will have been found statistically significant in Tracks 1 and 2. The project outcome will significantly advance and broaden the scientific knowledge in the field of visual comfort. Besides this important short-term impact, in the long run, the results will improve the design process through the use of more reliable metrics. And finally, users, employers, and owners will benefit from higher comfort and productivity, optimized building performance, and reduced energy demands.


Related publications

Jain, S., Karmann, C., & Wienold, J. (2021). Subjective assessment of visual comfort in a daylit workplace with an electrochromic glazed façade. Journal of Physics: Conference Series, 2042(1), 012179.

Jain, S., Karmann, C., & Wienold, J. (2022). Behind electrochromic glazing: Assessing user’s perception of glare from the sun in a controlled environment. Energy and Buildings, 256, 111738.

Jain, S., Wienold, J., & Andersen, M. (Eds.). (2021). Glare assessment in a daylit workplace from a physiological perspective. In ANFA 2021 SYMPOSIUM – QUANTIFIED BUILDINGS, QUANTIFIED SELF.

Jain, S., Wienold, J., & Andersen, M. (2022, November 23). Effect of window glazing color and transmittance on human visual comfort. PLEA 2022 SANTIAGO Will Cities Survive? Passive Low Energy Architecture, Santiago, Chile.

Karmann, C., Chinazzo, G., Schüler, A., Manwani, K., Wienold, J., & Andersen, M. (2023). User assessment of fabric shading devices with a low openness factor. Building and Environment, 228, 109707.


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