2015 Volume 99 Issue 1 Pages 20-24
Light exposure at night affects the human circadian system and is a possible cause of delayed sleep timing and circadian rhythm. It has been found that blue light has more impact on circadian rhythm and that even ordinary room light can suppress melatonin secretion at night. On the other hand, there is a large individual difference in light responsiveness. In order to recommend countermeasures and guidelines for light at night, it might be important to consider individual differences and the factors involved. In this paper, examples of inter- and intra-individual differences in the effects of light on circadian rhythm and melatonin secretion are introduced, and factors involved, including age, ethnicity, gene polymorphism and life style, are discussed.