AbstractWe tested whether the colour temperature of the illumination (realised through manipulating the ceiling light) impacted on thermal comfort, based on the hypothesis that a lower colour temperature is associated with feeling warmer and a higher colour temperature with feeling cooler. If confirmed, then light might be a tool for energy-saving through allowing ambient air temperatures to vary over a wider range and hence reducing the need for space heating and cooling.Testing took place in a climate chamber. In Study 1, comfort ratings were collected using thermal comfort surveys (N=32). In Study 2, an observational design was used, where changes in clothing level, interpreted as thermal discomfort responses, were observed (N=32). We compared comfort ratings and changes in clothing level under light with a colour temperature of 2700K vs. 6500K. Results partly confirmed the hypotheses: both self-report and observation indicated higher comfort under the low colour temperature. Further research will need to replicate findings in a real-world setting to see if light might indeed be a tool to modulate thermal comfort, and hence reduce usage of heating and cooling.