Exposure to light at night results in disruption of endogenous circadian rhythmicity and/or suppression of pineal melatonin, which can consequently lead to acute or chronic adverse health problems. In the present study, we investigated whether exposure to very dim light or very bright light for a short duration influences melatonin suppression, subjective sleepiness, and performance during exposure to constant moderately bright light. Twenty-four healthy male university students were divided into two experimental groups: Half of them (mean age: 20.0 ± 0.9 years) participated in an experiment for short-duration (10 min) light conditions of medium intensity light (430 lx, medium breaks) vs. very dim light (< 1 lx, dim breaks) and the other half (mean age: 21.3 ± 2.5 years) participated in an experiment for short-duration light conditions of medium intensity light (430 lx, medium breaks) vs. very bright light (4700 lx, bright breaks). Each simulated night shift consisting of 5 sets (each including 50-minute night work and 10-minute break) was performed from 01:00 to 06:00 h. The subjects were exposed to medium intensity light (550 lx) during the night work. Each 10-minute break was conducted every hour from 02:00 to 06:00 h. Salivary melatonin concentrations were measured, subjective sleepiness was assessed, the psychomotor vigilance task was performed at hourly intervals from 21:00 h until the end of the experiment. Compared to melatonin suppression between 04:00 and 06:00 h in the condition of medium breaks, the condition of dim breaks significantly promoted melatonin suppression and the condition of bright breaks significantly diminished melatonin suppression. However, there was no remarkable effect of either dim breaks or bright breaks on subjective sleepiness and performance of the psychomotor vigilance task. Our findings suggest that periodic exposure to light for short durations during exposure to a constant light environment affects the sensitivity of pineal melatonin to constant light depending on the difference between light intensities in the two light conditions (i.e., short light exposure vs. constant light exposure). Also, our findings indicate that exposure to light of various intensities at night could be a factor influencing the light-induced melatonin suppression in real night work settings.

晚上暴露在阳光下会导致内源性昼夜节律紊乱和/或松果体褪黑激素被抑制，从而可能导致急性或慢性不良健康问题。在本研究中，我们调查了在短时间内暴露于非常暗的光或非常明亮的光是否会影响褪黑激素的抑制，主观嗜睡以及在持续适度的中等明亮光下的表现。24名健康的男大学生被分为两个实验组：其中一半（平均年龄：20.0±0.9岁）参加了中等强度（430 lx，中等间歇）短时（10分钟）光照条件的实验）与非常昏暗的光线（<1 lx，昏暗的休息）和另一半（平均年龄：21.3±2）。5年）参加了一项针对中等强度光（430 lx，中等断裂）与非常强光（4700 lx，明亮断裂）的短时光照条件的实验。从01:00到06:00 h进行每个模拟的包括5组的夜班活动（每组包括50分钟的夜间工作和10分钟的休息时间）。在夜间工作期间，受试者被暴露于中等强度的光（550 lx）。从10：00到06:00，每小时每小时进行10分钟的休息。测量唾液中褪黑激素的浓度，评估主观嗜睡程度，从21:00小时到实验结束，每小时进行一次精神运动警惕任务。与中等休息条件下04:00至06:00 h的褪黑素抑制相比，昏暗休息的状况显着促进了褪黑激素的抑制，明亮休息的状况显着降低了褪黑激素的抑制。然而，昏昏欲睡或明亮休息对主观嗜睡和心理运动警觉任务的执行没有显着影响。我们的发现表明，在恒定光照环境下，短时间的周期性曝光会影响松果褪黑激素对恒定光照的敏感性，这取决于两种光照条件下的光强度之间的差异（即，短时间曝光与恒定时间曝光）。此外，我们的发现还表明，在夜间工作环境中，夜间暴露于各种强度的光可能是影响光诱导褪黑激素抑制的因素。