How does light intensity influence evening dressing behavior in the cold?

A review of the studies on nonvisual lighting effects in the field of physiological anthropology

Here, we review the history and the trends in the research on the nonvisual effect of light in the field of physiological anthropology. Research on the nonvisual effect of light in the field of physiological anthropology was pioneered by Sato and colleagues in the early 1990s. These authors found that the color temperature of light affected physiological functions in humans. The groundbreaking event with regard to the study of nonvisual effects of light was the discovery of the intrinsically photosensitive retinal ganglion cells in the mammalian retina in the early 2000s. The interest of the physiological anthropology scientific community in the nonvisual effects of light has been increasing since then. A total of 61 papers on nonvisual effects of light were published in the Journal of Physiological Anthropology (including its predecessor journals) until October 2018, 14 papers (1.4/year) in the decade from 1992 to 2001, 45 papers (2.8/year) in the 16 years between 2002 and 2017, and two papers in 2018 (January-October). The number of papers on this topic has been increasing in recent years. We categorized all papers according to light conditions, such as color temperature of light, light intensity, and monochromatic light. Among the 61 papers, 11 papers were related to color temperature, 20 papers were related to light intensity, 18 papers were related to monochromatic light, and 12 papers were classified as others. We provide an overview of these papers and mention future research prospects.

Influences of diurnal bright or dim light exposure on urine volume in humans

We investigated with eight healthy females if 8 hr diurnal (0700 to 1500 h) bright rather than dim light (5,000 vs. 80 lx) influenced urine volume. Environmental illuminance was made identical at all other times besides 07:00 to 15:00 h. The participants spent time at strictly regulated schedules in a bioclimatic chamber (26 degrees C, relative humidity 60%) for 57 h. Blood was drawn (2 ml) just before lunch in order to calculate Creatinine clearance (Ccr). Urine volume was significantly higher during wakefulness and the 8-h sleep period with bright rather than dim light. Ccr was significantly higher after bright light. The results were discussed in terms of suppression of the sympathetic nerve system under the influence of diurnal bright light exposure. We also discussed these in terms of physiological polymorphisms.

Effects of color temperature of illumination on physiological functions

This article presents our recent studies on the effects of color temperature on the taste sense and the influence of color temperature on bright light exposure during night rest period. Ten male Japanese and ten male Chinese were exposed to four illumination conditions (200, 1500 lx x 3000, 7500 K). Their taste threshold of four common tastes and amount of saliva were measured. It was found in both Japanese and Chinese subjects that sensitivities to sweet and bitter taste were decreased under the lower illuminance condition. Under the lower color temperature condition, sensitivity to bitter taste in Japanese and sweet taste in Chinese were decreased. Secretion of saliva increased under the lower illuminance condition in both Japanese and Chinese. Only in Chinese subjects, secretion of saliva increased under the lower color temperature condition. In a separate experiment, six male Japanese students were subjected to bright light exposure during a night rest period. They performed a mental task from 23:00 h till 02:00 h, and took a rest from 00:00 h to 01:00 h. During the rest period they were exposed to bright light (3000 lx) of three different color temperatures: 3000 K, 5000 K, and 7000 K. After exposure to bright light of 3000 K but not at other color temperatures, the EEG alpha1 band ratio and the beta band ratio at 02:00 h were higher and lower, respectively, than that at 01:00 h. These findings indicated that lower color temperature bright light exposure during a night rest break led to a reduction of subjects' arousal level during the subsequent work. Herein, we discuss these results from the viewpoint of physiological anthropology.