Influence of two different light intensities from 16:00 to 20:30 hours on evening dressing behavior in the cold.

The present experiment tested our hypothesis that the subjects will wear more clothing in the evening cold under the influence of bright light exposure in the late afternoon and evening. Nine young female adults participated in this study. Light intensity was controlled from 9:00 h to 16:00 h at 100 lx, and from 16:00 h to 20:30 h either at 3000 lx in the bright light (Brighte) or at 10 lx in the dim light ("Dim") conditions. Light intensity was maintained at 10 lx from 20:30 h to 23:00 h. They were instructed to wear garments to maintain themselves to feel comfortable during the fall of ambient temperature from 30 degrees C to 15 degrees C (21:00 h - 22:00 h) and its constant temperature at 15 degrees C (22:00 h - 23:00 h). Most subjects dressed in heavier clothing in the "Bright" than in the "Dim" conditions. The evening fall of core temperature was significantly smaller and the urinary melatonin secretion was significantly lower in the "Bright" condition, suggesting that the set-point of core temperature has been set at a higher level during the evening and at night, being influenced by the less amount of melatonin secretion. Thus, it is concluded that the late afternoon and evening bright light exposure could accelerate the dressing behavior in the evening cold.