2018 Volume 41 Pages 206-210
Bright nocturnal light has been known to suppress melatonin secretion. However, bright light exposure during daytime might reduce light-induced melatonin suppression (LIMS) at night. This study aims to evaluate the effect of high correlated color temperature LED light during daytime on LIMS. Male participants were exposed to different light conditions for 3 h in the morning (09:00–12:00). The light conditions were dim light (<10 lx), 125 lx high correlated color temperature (CCT) LED light, and 250 lx high CCT LED light. The subjects were then exposed to bright light (white light, 300 lx) for 1.5 h at night (01:00–02:30). Saliva samples were taken before (01:00) and after (02:30) exposure for evaluation of melatonin secretion. There were no significant differences in melatonin secretion before and after night-time light exposure on the 125 lx and 250 lx morning light conditions. Since these light intensities were almost equal to those in our previous study, the high CCT LED light might be appropriate for certain work places (e.g., hospitals and underground spaces), contributing to the reduction of our health risk and also saving energy.