Experiments by Penn State University researchers have shown that enriched white light that includes “invisible” blue and red wavelengths can directly affect a person’s perception of indoor temperature, including making a warm room feel more than one degree Fahrenheit cooler.
In future efforts, the Penn State team said they will explore the effect on different populations and in different environments, including under extreme hot and cold conditions. They also plan to evaluate the potential for incorporating color-enriched white lighting in real-world buildings where it may improve comfort and reduce energy use.
Enriched White Light Theory Builds on Previous Colored Light Discovery
According to a statement announcing the research, some previous studies have demonstrated that colored lighting can influence how hot or cold a room feels. For example, subjects in a previous study rated a room as warmer than it was when exposed to red light. Conversely, subjects described rooms bathed in blue light as feeling cooler.
However, the Penn State team notes, implementing red and blue lighting in most working spaces is impractical. Still, they wondered whether they could use the phenomenon to reduce the perception of heat or cold, thereby lowering energy costs for environmental control systems.
‘‘We wanted to understand whether lighting can widen people’s thermal comfort zone,” explained Penn State professor of architectural engineering and the principal investigator of the published study detailing the team’s findings. Julian Wang. “If it can, even a modest shift in perceived temperature can translate into substantial cumulative energy savings over time.’’
Due to the impracticality of colored lighting, the team explored the possibility of enriching the white light already used in office spaces and classrooms with red or blue wavelengths without affecting visibility
‘‘The novelty of this study is that we used white light that looks identical to the human eye but has a different spectral composition,’’ Wang explained.
Tests Reveal Temperature Perception Effect of Red and Blue Wavelengths
Instead of placing color-enriched white lights in actual offices, the team performed a series of experiments in a controlled indoor environment meant to simulate a typical office cubicle on the Penn State campus.
First, Wang and colleagues recruited five men and five women aged 18 to 35. Next, they placed each participant in the simulated office cubicle at an ambient air temperature of 76°F, then gradually increased and decreased the room’s air temperature in varying cycles.
To evaluate the effect of light on participants’ temperature perception, each subject was exposed to white light enriched with either blue short-wave light or red long-wave light. Critically, the lights appeared identical. Wang said that keeping the light appearance the same “allowed us to evaluate whether the response was driven by the spectral composition of the light, rather than by people’s perception of color.”
Throughout the entire process, the researchers monitored the participants’ thermal sensation and apparent comfort. The researchers also monitored the participants’ behavior.
As in previous studies, the color of the light waves appeared to have an effect even though they were effectively imperceptible to the participants. For example, when the participants were exposed to the blue-enriched white light, the researchers said, “they felt cool enough to tolerate air temperatures about 1.3 F warmer.” Conversely, when the participants were exposed to red-enriched white light, they felt warmer.
When discussing the results, Wang said the most critical point is that subtle color-enrichment differences hidden within ordinary white light can produce effects similar to pure-color lights without adversely affecting the work environment. Such effects could translate into real reductions in energy usage.
From Office Space to Space Habitats
In the future, Wang and colleagues plan to test the effect of color-enriched white light on a more diverse set of volunteers, including across more age groups.
‘‘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.
The Penn State team also plans to investigate the temperature-sensation-altering effects of color-enriched light in combination with other factors, such as sound, window views, and visual patterns. The team said they may also explore the effect of color-enriched light in more extreme conditions to “evaluate how they could be incorporated into real-world buildings to improve comfort while reducing energy use.”
‘‘Our long-term goal is to expand people’s multi-domain interactions, and if successful, this approach could improve comfort and human performance while reducing energy use in buildings, from homes and offices to space habitats,” Wang said, adding that ‘‘this is just one of our starting points.”
The study “Effects of metameric light on human subjective and behavioral thermal responses in daytime transient thermal environments” was published in Energy and Buildings.
Christopher Plain is a Science Fiction and Fantasy novelist and has spent the last six years as Associate News Editor and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him at christopher@thedebrief.org.