Influence of Light Intensities on Clothing Behavior and Melatonin Secretion

The intent of this study was to determine whether different light exposure could modify the clothing behavior in the evening cold environment or not. Nine female subjects volunteered to this study. In a bright light or a dim light condition, light intensity was controlled 3000 lx or 10 lx respectively. Subjects were introduced to wear various kinds of garments whenever they need to feel comfortable as the room temperature began to decrease. The room temperature was lowered from $30^{\circ}C$ to $15^{\circ}C$ for one hour (21:00 h~22:00 h) and maintained at $15^{\circ}C$ for additional one hour (22:00 h~23:00 h). Subjects stayed in chamber from 08:00 to the next day 07:00. Clothing behavior, core temperature, subjective temperature sensation and melatonin secretion were measured. Most subjects put on the clothing more quickly and more thickerly in the bright light rather than in the dim light condition. The fall of core temperature during night was significantly less under the bright light in the late afternoon, suggesting that the set-point of core temperature has been set at a higher level during the evening and the night, being supported by the less amount of melatonin secretion. Thus, it is concluded that the quicker dressing behavior with thicker clothing in the "Bright" condition is advantageous in evening cold exposure, since it enables the core temperature to reach its set-point value more easily.

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