Physiological Effects of Sudden Change in Illuminance during Dark-Adapted State

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To derive an optimal illuminance of nighttime illumination, we conducted an experiment with 7 healthy young individuals and 7 healthy elderly individuals as subjects. After 20 minutes of adaptation to darkness, subjects were exposed to illumination under 5 conditions comprising 0.5lx, 1lx, 3lx, 10lx, or 30lx vertical illuminance of the facial region, and heart rate variability (HRV) and electroencephalogram (EEG) were measured, and discomfort was evaluated by subjective report. Results of LF/(LF+HF) (LF=low frequency, HF=high frequency) demonstrated a V-shaped trend for the young groups beginning during exposure and ending post exposure, with 3lx conditions representing the minimum value, a value markedly lower than that for 30lx conditions. From these results we inferred that approximately 3lx illuminance could best suppress physiological stress. Evaluation of discomfort by subjective report also demonstrated an increase in discomfort evaluation scores under high illuminance conditions. The α-wave proportion of EEG during exposure fell markedly on 3lx or higher illuminance conditions, and we inferred that visual sensory information and cortical activity level were adequately attained in 3lx or higher illuminance conditions. These results suggest that the optimal illuminance of nighttime illumination is approximately 3lx.
日本生理人類学会の論文