Does glazing color influence our perception of discomfort glare from daylight?

Spectrum and correlated colour temperature of light are shown to influence human visual comfort. Previous research conducted with electric light, mainly in the context of vehicular headlamps, have demonstrated that coloured LEDs induce more discomfort glare than white LED and among the coloured LEDs blue ones gave the highest glare perception[1]–[3]. However, there are currently no studies that determine the influence of filtered daylight on discomfort glare in context of daylit indoor spaces which can prove valuable for building façade industry. The spectral power distribution of the daylight inside a space can vary depending on the glazing spectrum. With the current trend of tinted glazing such as electrochromic (EC) glazing and dye-sensitized solar cell glazing that alters the spectrum of daylight, there is a need to extend these results under daylit conditions. To address this gap, we conducted a between subject study investigating the effect of glazing color on occupants’ glare perception under blue-tinted EC glazing (20 participants) and color-neutral glazing systems (55 participants), both widely employed in commercial buildings. We exposed the participants to four visual scenarios with different low glazing transmittances and the sun as the only glare source visible through the glazing. The tests were conducted in a semi-controlled office-like test room with daylight as the only source of light. The glazing’s spectral transmittances were experimentally determined in a dedicated glazing and nanotechnology lab facility. During the exposure time, participants were given a typing task that allowed them to visually adapt to each experimental scenario. Afterwards, participants filled a questionnaire indicating their level of visual comfort. We captured high dynamic range images of each experimental scenario from participant’s eye position to record the scene luminance and calculate various daylight glare metrics. Comparing participant’s responses to glare, we found that through color-neutral glazing of various transmittances, the reported level of discomfort was similar to EC glazing for twice the sun disc’s luminance, thereby indicating that glare was perceived stronger for a blue-colored glare source. This outcome questions whether we measure the luminance and glazing transmittance correctly under tinted glazing scenarios, since the standard way of measuring photometric quantities uses the CIE V2() function for 2-degree standard observer but falls short of explaining the enhanced glare sensitivity under shorter wavelengths. To further delve into this question, we applied the standard CIE V10() sensitivity curve along with earlier proposed luminous efficiency functions for discomfort glare and compared them in terms of their ability to account for differences in the perceived discomfort glare. The results showed that none of these luminous efficiency functions can explain the increased sensitivity for blue-colored glare source that was found, which indicated that its cause should be sought elsewhere. Based on the results, we provide recommendations towards the transmission thresholds for switchable glazing to prevent glare risks when sun is in the field of view. Outcomes of this study can be further implemented to the future development goals for switchable glazing systems and architectural façade design application in achieving visually comfortable spaces. References: [1] Y. Yang, R. M. Luo, and W. Huang, “Assessing glare, Part 3: Glare sources having different colours,” Lighting Research & Technology, vol. 50, no. 4, pp. 596–615, Jun. 2018, doi: 10.1177/1477153516676640. [2] M. Sivak, B. Schoettle, T. Minoda, and M. J. Flannagan, “Short-Wavelength Content of LED Headlamps and Discomfort Glare,” The Journal of the Illuminating Engineering Society, vol. 2, pp. 145–154, 2005, doi: 10.1582/LEUKOS.2005.02.02.006. [3] J. Fekete, C. Sik-Lányi, and J. Schanda, “Spectral discomfort glare sensitivity investigations,” Ophthalmic and Physiological Optics, vol. 30, no. 2, pp. 182–187, Mar. 2010, doi: 10.1111/j.1475-1313.2009.00696.x.