Influence of lighting colour temperature on indoor thermal perception: A strategy to save energy from the HVAC installations

Abstract

This paper examines how the lighting colour temperature affects indoor thermal comfort. A test room with three separate environments was set and, in each one of them, a lamp with a different colour temperature was positioned to evaluate the influence of a cold, neutral and warm light. The colour temperatures of the used lamps were 11,530 K, 4,000 K and 1,772 K respectively. During each test, while complying with the EN 12464-1, a lighting level of 500 lx and a uniformity coefficient higher than or equal to 0.7 were maintained. With an air temperature of about 22 °C, 42 people were interviewed and filled a questionnaire structured according to the ISO 10551 to judge the resulting thermal comfort. The study reported a certain influence of the lighting colour temperature on people's thermal perception which was only lower than the one related to the gender. With respect to the ASHRAE 7-point scale, being exposed to the different types of light led to a decrease (0.44 units under cold light) in the mean value of the votes given by the interviewees to judge their thermal perception. Such condition gives the possibility to increase, without varying the thermal perception of the subjects, the air temperature of 1.25 °C, 0.46 °C and 0.23 °C with cold, neutral and warm light respectively. Finally a cross tabulation analysis was performed to compare the votes of the participants before and after they were exposed to the different lights with those predicted by the Predicted Mean Vote (PMV).