Sneha Jain

Biographie

Sneha Jain is currently conducting her PhD thesis on the influence of ocular characteristics and colour of light on discomfort glare from daylight at workplaces. She completed her undergraduate degree in architecture and has a Master of Science in Building Science from International Institute of Information Technology in Hyderabad, India. Her Master thesis was on Daylight glare estimation for open-loop window roller shade control system to optimize daylight levels and visual comfort in a lab setup. She also worked as a research fellow at Lawrence Berkeley National Lab in Berkeley, California. Her current work focuses on improving the prediction of current discomfort glare models.

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Discomfort glare from daylight: Influence of transmitted color and the eye's macular pigment

Sneha Jain

Designing architectural façades that allow sufficient daylight to create visually comfortable and pleasantenvironments is a challenging aspect of building design. It requires accounting for visual comfort anddiscomfort glare risks and understanding the factors that influence them. In the last two decades, severalprediction models have been developed to quantify discomfort glare by considering almost exclusivelythe photometric properties and spatial distribution of incoming light. Although these empirical modelshave been derived to best match one's perception of glare, they fail to account for the significant interindividualvariability that exists in glare perception and are furthermore limited in their applicability incertain visual environments. It is evident from the literature that not all the factors influencingdiscomfort glare perception are known and accounted for in the existing prediction models. Based onthe literature review, we have identified two potential factors, namely, the macular pigment density inthe retina and the color of daylight, as likely to influence discomfort glare perception. Up to now, theirinfluence on glare induced by daylight has remained unknown.To address this gap, this thesis aims to determine the influence of macular pigment density and color ofthe sun disc (altered by colored glazing) on discomfort glare perception in daylit environments. Bymeans of three psychophysical experiments conducted in office-like test rooms along with the ocularexaminations of the participants, we determined the influence of macular pigment and color of daylighton the perception of discomfort glare for young and healthy individuals. Three experiments wereconducted, one with blue electrochromic glazing, one with color-neutral glazing, and the third with red,blue, green, and color-neutral glazing. Each experiment followed a similar protocol of exposing everyparticipant to four daylight glare scenarios and recording their responses to questionnaires. The fourdaylight scenarios differed either in color or in the transmittance of the glazing through which the sunwas visible as the primary glare source. The remaining windows were set in a way to keep the overallcolor rendering in the space as neutral as possible.The results show that macular pigment density does not influence discomfort glare perception from thesun disc filtered by color-neutral glazing in the near-peripheral field of view. However, when exposedto the sun disc filtered by saturated blue-colored glazing also in the near-peripheral field, participantswith higher macular pigment density were better able to tolerate the glare, indicating a significantinfluence of macular pigment in this case.In regards to the influence of color, results show that the perceived color of the sun disc (as filtered bycolored glazing) has a strong influence on participants' perception of glare. Direct sunlight filteredthrough four types of colored glazing of a similar visible (photopic) transmittance caused significantlydifferent levels of discomfort glare perception amongst the participants. More precisely, participantsexperienced statistically higher levels of glare under the red and blue glazing compared to the colorneutralor green glazing.The findings show that the photopic luminosity function (V2°(l)) is not an appropriate weightingfunction to characterize the spectral sensitivity of the human eye when a high-intensity colored glaresource is in

EPFL2023

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Perceived glare from the sun behind tinted glazing: Comparing blue vs. color-neutral tints

Marilyne Andersen, Sneha Jain, Maxime Lagier, Andreas Schueler, Jan Wienold

While the influence of a glare source's spectrum on sensitivity to discomfort glare has been demonstrated repeatedly under electric light conditions, it has not yet been studied under actual daylit conditions. To investigate the influence of spectral alterations of the sun disc on glare perception when seen behind a colored glazing, we performed a cross-evaluation of occupants' visual comfort in a space either daylit through blue-tinted electrochromic (EC) glazing (20 participants) or through color-neutral glazing (55 participants), having selected two types of glazing that are widely employed in commercial buildings. Under both types of glazing, participants experienced four glare scenarios presenting different glazing transmittances (from low to extremely low) in which the sun was the only glare source visible. Comparing the participants' responses to glare, we found that participants experienced discomfort more often in blue-tinted glazing compared to color-neutral glazing, even though glare metrics would have predicted higher levels of discomfort in these latter cases. This indicates that participants basically tolerated glare better under color-neutral daylit conditions compared to blue-colored conditions. To explain our findings, we considered four spectral discomfort glare sensitivity functions that have previously been proposed to replace the standard CIE V2°(λ) and applied them to the DGP and CGI glare metrics. However, none of these adjustments to glare metrics made any difference to our findings, which consistently showed an increased glare sensitivity under shorter wavelengths, indicating that its cause should be sought elsewhere. Some hypotheses are formulated at the end of the paper in this regard.

2023

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The spectral sensitivity of the average human eye in photopic conditions is represented by the photopic luminosity function V (λ). The CIE has established the photopic luminosity functions for the 2o and 10o visual fields for a standard observer applicable for foveal and para-foveal light sources, respectively. These functions differ in short wavelength region where V10° (λ) has higher sensitivity. However, V10°-(λ) function is not implemented in any of the discomfort glare metrics even though, for most glare scenarios, the glare source is located further than 2o from the fovea. This can result in an underestimation of the short wavelength contribution of the glare sources’ spectra, and, a fortiori, in the blue-colored light sources. In this paper, we aim to determine the impact of replacing V2° (λ) with V10°-(λ) in the daylight discomfort glare metrics for scenarios where the visible sun disk lies very much outside the 2° zone and acts as a glare source through blue-tinted and color-neutral tinted low transmittance glazing. We compare three types of colored glazed façade: color-neutral glazing, blue-tinted electrochromic (EC) glazing and an extreme case of saturated blue-tinted glazing. We found that the difference in derived glare source luminance and discomfort glare metrics is statistically significant only for the saturated blue glazing with an average 70% increase in luminance and 20% increase in DGP (i.e. one category higher discomfort) and 9% increase in CGI, when using V10° (λ). We conclude that the impact of replacing V2° (λ) with V10°-(λ) is negligible for standard EC or color-neutral glazing types in commercial buildings. However, specific cases of saturated blue light sources that peaks at 450nm are more accurately quantified by V10° (λ), that produces higher values of glare metrics.

2022

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Discomfort glare from daylight: Influence of transmitted color and the eye's macular pigment

Sneha Jain

EPFL2023