The spectrum of indoor lighting plays a role in how people perceive temperature, according to research led by scientists at Penn State. In a study published in the August 2026 issue of the journal Energy and Buildings, researchers found that controlling the red and blue wavelengths of white light can impact how people experience indoor temperatures. Red and blue wavelengths are two of the bandwidths of electromagnetic radiation that flow through space and are perceived by humans as light.
"We wanted to understand whether lighting can widen people's thermal comfort zone," said Julian Wang, professor of architectural engineering at Penn State and principal investigator of the study. He said this was an exploratory study. "The next step is to do research in a larger and more diverse population to determine whether these effects extend beyond young adults and could be applied globally," Wang said.
Previous studies have shown that colored lighting, such as blue and red light, can influence thermal perception, he said. However, colored lighting is impractical for everyday environments such as offices, classrooms, and homes because it can be visually distracting and create visual noise, making it difficult to perform routine tasks comfortably.
Through this project, Wang's team found that the "color" doesn't need to be visible — subtle differences hidden within ordinary white light can produce similar effects without changing how the lighting looks.
"We used white light that looks identical to the human eye but has a different spectral composition," Wang said. "That allowed us to evaluate whether the response was driven by the spectral composition of the light, rather than by people's perception of color."
To test this idea, the researchers recruited 10 participants, five women and five men, between the ages of 18 and 35. Participants occupied a simulated office cubicle inside a climate-controlled chamber at Penn State's University Park campus while experiencing gradually increasing and decreasing air temperature cycles starting from an initial room temperature of approximately 76 degrees Fahrenheit (about 24 degrees Celsius).
During the separate experimental sessions, participants were exposed to two types of white light that looked identical but differed in their dominant wavelengths: one enriched in blue short-wave light and the other enriched in red long-wave light. Throughout the study, the researchers monitored participants' thermal sensation, comfort and behavioral responses.
The researchers found that when participants were exposed to blue-enriched white light in the controlled room, they tolerated air temperatures about 1.3 degrees Fahrenheit (about 0.7 degrees Celsius) warmer. In contrast, red-enriched white light had the opposite effect.
The team said it also hopes to investigate how lighting interacts with other environmental factors, such as sound, window views and visual patterns, to shape people's perception of indoor comfort.