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

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.