Introduction: A Glare That Defies Expectations
Glare from sunlight is a common problem for occupants of modern buildings, often worsened by windows with insufficient shading. Traditional smart glazing aims to curb overheating in summer while reducing glare by adjusting tint levels. Most of these glazing technologies trend toward a blue tint when shading increases. However, a recent study from EPFL’s Laboratory of Integrated Performance in Design (LIPID) challenges long-standing assumptions about how we perceive glare and how it should be measured.
Challenging the V(λ) Spectral Sensitivity Function
Light measurements and evaluations—ranging from light levels to perceived glare and even material properties—have historically been anchored to the spectral sensitivity function V(λ). This function, developed over a century ago, represents average human eye sensitivity across wavelengths. The new research from LIPID, supported by the Swiss National Science Foundation (SNSF) and published in Scientific Reports, suggests that V(λ) may not accurately reflect human perception under colored lighting. The findings imply that current glare models might not fully capture how people experience glare from colored glazing in real-world conditions.
Red Light: The Unexpected Culprit
Prevailing wisdom, largely built on studies of blue light and automotive LED headlights, indicated that blue wavelengths are notably more discomforting at equal brightness. The LIPID study, led by Sneha Jain during her PhD, tested four glare conditions—red, blue, green, and neutral—using glazing with different color filters under both low and high daylight intensities. Surprisingly, participants reported the red-glazed condition as the most disturbing source of glare, followed by blue and then green. This order directly contradicts traditional expectations and highlights a potential flaw in standard glare assessment methods.
What this means for visibility and comfort
The observed prominence of red glare suggests that the way we quantify and interpret glare should include colorimetric analysis, especially for strongly colored light sources. Relying solely on photometric approaches—those focused on luminance and intensity—could yield glare estimations that deviate by more than 50% from human perception in colored-light scenarios.
Implications for Glazing Technology and Standards
The study’s authors argue that current glare models are not fully reliable and call for integrating colorimetric measurements into standard practice. In practical terms, this could influence how future smart glazing devices are designed and controlled. If red-changing glazing is perceived as more glare-inducing than previously thought, designers may need to rethink tinting strategies, control algorithms, and the color footprint of glazing to optimize visual comfort without sacrificing energy performance.
Towards Smarter Glazing and Lighting Systems
Beyond glazing hardware, the findings could shape the broader field of lighting design, including LED systems capable of producing colored light. By acknowledging the perceptual effects of red and other colors, researchers and manufacturers can develop smarter, more comfortable lighting and shading solutions that align better with human perception. This aligns with a growing movement toward user-centered design in architectural environments, where comfort, productivity, and well-being are prioritized.
Next Steps: Expanding the Research
Building on these preliminary results, Jan Wienold, LIPID’s research and teaching associate, is spearheading a new four-year, SNSF-funded project to expand the investigation. The team plans to test additional colors and employ diverse experimental methods to quantify the observed effects more comprehensively. The goal is to adjust glare models and upgrade design standards so that they reflect the nuanced ways colored light interacts with human vision.
Practical Takeaways for Building Designers
- Recognize that glare is not purely a photometric phenomenon; color plays a significant role in perceived glare.
- Incorporate colorimetric analysis into glare assessment for highly tinted or colored glazing.
- Consider adaptive shading strategies that account for red-tinted glare during certain times of day or in certain climates.
- Monitor updates to standards and guidance as the field evolves with new research outcomes.
As the modeling of glare evolves, architects and building operators can expect smarter glazing that reduces discomfort while maintaining daylighting and energy efficiency. The intersection of color science and human perception promises a more comfortable, better-lit built environment for occupants around the world.
