EPFL studies connection between glare color and discomfort

14 Oct 2025

Effects of different glazing suggest models of indoor environments may need refining.

A project at Swiss research center EPFL has studied how the discomfort caused by glare from daylight is influenced by the color of that glare.

The connection between color and comfort has been extensively studied for electric lighting, where the findings were that people perceive glare more strongly under blue-colored LEDs.

But the same links have not been studied for daylight illumination, according to EPFL. This makes it more difficult to predict and mitigate glare in built environments, where colored glazing and filtered daylight are widely encountered.

The findings, discussed in Scientific Reports, have implications for building standards and research, as well as for the comfort of workers and occupants.

"Glare from sunlight can be a major source of discomfort for building occupants, especially when the windows have inadequate shadings," commented the EPFL project.

"New smart glazing technology aims to provide protection from overheating in summer and from glare by changing the tint level to reduce the amount of solar radiation that passes through. Most of these glazing types change their color to blue while tinting."

The increasing use of colored building-integrated photovoltaics, or BIPV, in building facades is another factor giving the determination of discomfort glare a practical current significance, noted the team in its paper. Colored glass that is highly efficient in terms of power generation, such as blue, can be less efficient in terms of visual comfort requirements.

This makes it necessary to know how the spectral shifts in daylight caused by colored glass facades may impact the perception of discomfort from glare.

Seeing red

The EPFL study involved participants sitting inside a controlled daylit office where the sun shone through colored glazing. They were exposed to four glare conditions - red, blue, green and neutral - created by different color filters in the glazing, for both low-intensity and high-intensity daylight.

The participants unanimously reported that the red glazing resulted in the most disturbing amount of glare, followed by blue and, to a lesser extent, green. This goes against the prevailing findings from study of automotive headlights that only blue light causes more discomfort than white light of the same intensity.

"The glare from red glazing was a real surprise because it contradicts the literature," said Jan Wienold from EPFL Laboratory of Integrated Performance in Design (LIPID).

"Our results show that current glare models aren’t fully reliable and that colorimetric methods should be used for strongly colored light sources and glazing. The photometric approach employed in today’s standards can produce deviations of more than 50 percent in glare estimations."

The optical properties of glazing are currently evaluated using a spectral sensitivity function, V(λ), intended to describe the average human eye's perception and sensitivity to light across different wavelengths. But the new EPFL results suggest that these current glare models may need to be changed.

"This finding challenges the current understanding of visual comfort and suggests that the mechanism driving the glare perception are not fully captured by current models," wrote the project. "An important practical takeaway of this study is that discomfort glare can likely be minimized by avoiding saturated red and blue colored glazing."