Study finds light spectrum shapes perception of indoor temperature

Researchers at Penn State University have found that subtle differences in the spectrum of white light can alter how warm or cool a room feels, creating a gap of about 1 degree Celsius between perceived and actual temperature. Published in the journal Energy and Buildings, the study tested 10 participants aged 18 to 35 in a controlled climate chamber designed to resemble an office. The room was initially set to roughly 24°C, and air temperature was gradually adjusted while participants were exposed to two types of white light that appeared identical but differed in their wavelength composition — one enriched with short-wavelength blue light and the other with long-wavelength red light. Their thermal perception, comfort levels and behavioral responses were recorded. Under the blue-enriched white light, participants reported feeling cooler and said they could tolerate an indoor temperature about 0.7°C higher than under the red-enriched lighting, which accelerated sensations of warmth. The researchers said the findings could inform lighting design in ways that reduce heating and cooling demand in buildings. The team added that follow-up studies are planned to extend the work to different age groups and to account for additional environmental factors such as sound, views and interior design.