Influence of bright light exposure for several hours during the daytime on cutaneous vasodilatation and local sweating induced by an exercise heat load.

The aim of the present study was to investigate the effect of exposure to differing light intensities for several hours during the daytime on the cutaneous vasodilatation and local forearm sweat rate induced by exercise. Seven healthy female subjects were exposed to bright light of 6000 lux (bright) or dim light of 100 lux (dim) during the daytime between 0900 hours to 1330 hours, followed by exposure to 150 lux until the test was over at 1600 hours. They spent their time in neutral conditions (29 degrees C, 40% relative humidity) from 0900 hours to 1500 hours, and then exercised on a cycle ergometer for 30 min at 50% maximal physical work capacity. Average tympanic temperatures were significantly lower in bright than in dim from 1133 hours to 1430 hours. The onset of cutaneous vasodilatation and local forearm sweating occurred at significantly lower tympanic temperature (Tty) during exercise after bright than after dim. After exercise, the cessation of forearm sweating and the rapid change of skin blood flow occurred at significantly lower Tty after bright than after dim. It was concluded that exposure to bright light over several hours during the daytime could reduce Tty and shift the threshold Tty for cutaneous vasodilatation and forearm sweating to a lower level.