Four minutes might not be enough for light colour temperature to affect sleepiness,mental effort,and light ratings

Abstract

Light exerts a number of non-image-forming effects that are mostly apparent during night-time but can also been seen during daytime. Recently, we have shown that exposure to light of higher colour temperature prior to performing a cognitive task leads to a weaker effort-related cardiovascular response compared to exposure to light of lower colour temperature. This present study tested if presenting light of different colour temperatures during rather than before the task performance would lead to equivalent changes in effort mobilization. Participants performed a modified Sternberg short-memory task for eight minutes as lighting conditions were adjusted to one of four experimental lighting conditions (2800 K, 4000 K, 5000 K, or 6500 K) after the first four minutes, for the remaining four minutes. We predicted that effort-related cardiovascular response would strengthen with decreasing colour temperature. The results, however, did not follow this predicted pattern. No significant effects of lighting conditions on subjective measures were observed. Therefore, we conclude that four minutes might not be enough for light colour temperature to induce changes in effort-related cardiovascular response or affect subjective ratings of sleepiness and lighting.