Time-of-Day-Dependent Effects of Monochromatic Light Exposure on Human Autonomic Nervous System

Abstract

We report the time-of-day-dependent effects of monochromatic lights at wavelength of 458 nm and 550 nm on human physiological and psychological parameters under the same irradiance density (9.8 µW/cm2 at eye level). We conducted an experiment in the daytime and nighttime on different days. Twelve subjects were selected, none of whom was either a morning-type or evening-type person, as assessed by the morningness/eveningness questionnaire. We found that 458 nm light exposure caused a greater high-frequency (HF)/(HF+low-frequency (LF)) component than did 550 nm light. The change of oral temperature (ΔTor) during exposure to 458 nm light was larger than that to 550 nm light in the daytime. Our findings indicate that short-wavelength monochromatic light can affect the circadian rhythms of autonomic nerve function and body temperature.