Visual alliesthesia--cloth color preference in the evening under the influence of different light intensities during the daytime.

The primary purpose of this study was to determine the effect of bright and dim light exposure during the daytime on cloth color preference in the evening. Ten healthy female volunteers were exposed to bright light of 5000 lx ("Bright") or dim light of 200 lx ("Dim") from 0730 +/- 1 h to 1800 hours, 200 lx from 1800 hours to 2330 +/- 1 h, and complete darkness during the sleep period (2330 hours +/- 1 h to 0730 +/- 1 h). The subjects were instructed to select the most preferable single one out of 41 cloth colors (24 x 52 cm, 100% cotton), every 5 min from 2100 hours to 2200 hours. Most subjects preferred a warmer cloth color in the Dim condition. The rectal temperature showed clear circadian rhythm both under Bright and Dim conditions but it was significantly lower during sleep in the Bright condition. On the contrary, leg skin temperature was significantly higher during the evening and sleep in the Bright. It is concluded that warmer cloth color is preferred in the evening after Dim condition at an ambient temperature, being based on the higher set point of core temperature after Dim.