With civilized environments in modern society, since the people tend to depend more on artificial illumination than on natural illumination which makes less discrepancy between day and night life, clarifying the relationship between human life and illumination is necessary. In our previous studies, we found that the subjects dressed faster with thicker clothing in the morning than in the evening when the room temperature decreased from 30°C to 15°C over 1 hour. We considered these results in terms of load error between the actual and set-point values in the core temperature. The present study was designed to examine the effect of bright light (3, 000 lx) / dim light (50 lx) exposure (09:30 h-14:30 h) on dressing behavior and thermoregulatory responses in the elderly people during the afternoon cold exposure. Five female subjects were instructed to dress to feel comfortable when the room temperature was decreased from 30°C to 15°C (15:00 h-17:00 h). The subjects felt cooler and dressed more quickly with thicker clothing after dim light exposure, it is conceivable that the set-point value of core temperature is reduced under the bright light condition. We discussed these results in terms of the establishment of set-point values in the core temperature at bright light condition. If the set-point of the core temperature is lower in the bright than in the dim light condition in present experiment, the dressing behavior with thinner clothing in the bright light condition is advantageous, since it enables the core temperature to reach its set-point value more easily.