The effect of correlated colour temperature of lighting on thermal sensation and thermal comfort in a simulated indoor workplace

Abstract

The ‘hue-heat’ hypothesis states that an environment which has wavelengths predominantly toward the red end of the visual spectrum feels ‘warm’ and one with wavelengths mainly toward the blue end feels ‘cool’. In order to test the hypothesis and to study the impacts of the correlated colour temperature of a light source on thermal sensation and thermal comfort, a study was conducted in a test room illuminated with an Light Emitting Diode (LED) lighting system with an adjustable correlated colour temperature where air temperature, air velocity, and relative humidity were kept constant. The correlated colour temperature of lighting inside the test room was changed gradually while keeping the colour rendering index values greater than 90, an illuminance level of 500 lx, and chromaticity difference (Duv) values within the limits of ±0.005. Sixteen study subjects were exposed to a ‘high room temperature’ (25℃) and a ‘low room temperature’ (20℃) on different days. The subjects were adapted to low correlated colour temperature (2700 K), medium correlated colour temperature (4000 K), and high correlated colour temperature (6200 K) lighting for 10 min and subsequently completed the questionnaire about their thermal comfort and thermal sensation. The results of this survey did not provide support for the hue-heat hypothesis and indicated that people felt thermally more comfortable in an indoor workplace at the correlated colour temperature of 4000 K than at the correlated colour temperature of 2700 K or 6200 K.

Interactions between the perception of light and temperature

“…This implies that thermal discomfort could be alleviated by changes in light conditions that improve (subjective) visual comfort, or, stated differently, that light conditions with a poor visual comfort could have a negative effect on thermal comfort. Baniya et al., 2016, also observed the highest thermal comfort ratings for the light condition that was perceived as being visually most comfortable . In the current study, the ambient temperature influenced the effect of light exposure on thermal comfort; the correlations between Δ visual comfort and Δ thermal comfort were only present during the cool and warm condition, not during the thermoneutral condition.…”

“…Therefore, it could be that even though the perceived color significantly differed between the 2700 K and 5800 K sessions, this difference in perceived color was too small to affect thermal sensation or thermal comfort. The light intensity can influence the hue‐heat effect, but the literature is not conclusive in this respect . Unfortunately, not all studies testing the hue‐heat hypothesis reported the light intensity that was used during the experiments .…”

“…6 Baniya et al (2016) did not find direct evidence for the hue-heat hypothesis although participants felt thermally more comfortable under light with a correlated color temperature (CCT) of their preference. 7 Fewer studies have been carried out on the direct effect of light intensity on thermal sensation and thermal comfort. Two studies found a cooler thermal sensation under low light intensity as compared to bright light, 8,9 while the third experiment reported no significant effect of light intensity on thermal comfort and thermal sensation.…”

“…The light intensity can influence the hue-heat effect, but the literature is not conclusive in this respect. 6,7 Unfortunately, not all studies testing the hue-heat hypothesis reported the light intensity that was used during the experiments. 31 Also, the duration of exposure could play a role, as, in the aircraft studies, the effect was measured after only 10 min of light exposure.…”

“…(2016) also found evidence for this hypothesis; thermal comfort ratings were higher when participants were exposed to 2700 K compared to 6500 K light, but concluded that more research is required to determine its practical value . Baniya et al (2016) did not find direct evidence for the hue‐heat hypothesis although participants felt thermally more comfortable under light with a correlated color temperature (CCT) of their preference . Fewer studies have been carried out on the direct effect of light intensity on thermal sensation and thermal comfort.…”