Fig. 3

Changes in the illuminance level that the participants were exposed to for 24 h in Japan (n = 54) and China (n = 58) (A). The illuminance on the vertical axis is displayed in logarithm. Average illuminance levels from midnight to early morning (0:00–6:00), in the morning (6:00–12:00), in the afternoon (12:00–18:00), and in the evening (18:00–24:00) (B). Data are shown as averages and standard deviations. (*p < 0.05, **p < 0.01)