The effects of exposure in the morning to light of different color temperatures on the behavior of core temperature and melatonin secretion in humans

Abstract

The quicker rise of core temperature after getting up would better prepare the individual for morning activity and feeling fresh on awakening. The present paper investigates how the lighting environment in the morning should be designed for better morning activity. We measured core temperature and salivary melatonin secretion as markers of circadian phase. Four females and five males served as the participants; aged from 22 to 24 years (mean = 23 years). On the experimental day, the participants were required to rise two hours after their minimum rectal temperature and were then exposed to the three kinds of lighting for two hours. The light conditions were (1) control light (dim light < 50 lux), (2) light of a high color temperature (6480 K, 2,500 lux) and (3) light of a low color temperature (3150 K, 2500 lux). The rise of rectal temperature was not significantly different between control and low color temperature lighting, but it was significantly different between control and high color temperature lighting, and between high and low color temperature lighting (p < 0.01). The decrease of melatonin was also significantly different (p < 0.01) between control lighting and lighting of a high color temperature, and between high and low color temperature lighting. Thus, it is concluded that the rise of core temperature and the fall of melatonin secretion in the morning could be accelerated by exposure to light of a high color temperature.