Effects of day-time exposure to different light intensities on light-induced melatonin suppression at night

Tomoaki Kozaki, Ayaka Kubokawa, Ryunosuke Taketomi, Keisuke Hatae

    Research output: Contribution to journalArticlepeer-review

    24 Citations (Scopus)


    Background: Bright nocturnal light has been known to suppress melatonin secretion. However, bright light exposure during the day-time might reduce light-induced melatonin suppression (LIMS) at night. The effective proportion of day-time light to night-time light is unclear; however, only a few studies on accurately controlling both day- and night-time conditions have been conducted. This study aims to evaluate the effect of different day-time light intensities on LIMS. Methods: Twelve male subjects between the ages of 19 and 23 years (mean ± S.D., 20.8 ± 1.1) gave informed consent to participate in this study. They were exposed to various light conditions (<10, 100, 300, 900 and 2700 lx) between the hours of 09:00 and 12:00 (day-time light conditions). They were then exposed to bright light (300 lx) again between 01:00 and 02:30 (night-time light exposure). They provided saliva samples before (00:55) and after night-time light exposure (02:30). Results: A one-tailed paired t test yielded significant decrements of melatonin concentration after night-time light exposure under day-time dim, 100- and 300-lx light conditions. No significant differences exist in melatonin concentration between pre- and post-night-time light exposure under day-time 900- and 2700-lx light conditions. Conclusions: Present findings suggest the amount of light exposure needed to prevent LIMS caused by ordinary nocturnal light in individuals who have a general life rhythm (sleep/wake schedule). These findings may be useful in implementing artificial light environments for humans in, for example, hospitals and underground shopping malls.

    Original languageEnglish
    Article number27
    JournalJournal of physiological anthropology
    Issue number1
    Publication statusPublished - Jul 4 2015

    All Science Journal Classification (ASJC) codes

    • Human Factors and Ergonomics
    • Physiology
    • Orthopedics and Sports Medicine
    • Anthropology
    • Public Health, Environmental and Occupational Health
    • Physiology (medical)


    Dive into the research topics of 'Effects of day-time exposure to different light intensities on light-induced melatonin suppression at night'. Together they form a unique fingerprint.

    Cite this