Effects of constant, intermittent, and dynamic lighting on human alertness and circadian rhythms: A controlled study...

Preventing fatigue and improving alertness are crucial for ensuring worker safety. Light exposure affects alertness, circadian rhythms, and behavioral performance. Although several recent studies have investigated these effects, their results have been inconsistent. This study determined optimal indoor lighting conditions by conducting a three-factor mixed crossover experiment to assess the daytime alertness of 147 college student participants (mean age: 20.82 ± 0.87 years) over a 16-h period under different lighting modes (constant, intermittent, and dynamic), lighting exposure time blocks (6:30-8:30, 8:30-10:30, 13:30-15:30, 17:30-19:30, and 19:30-21:30), and test times. Subjective sleepiness, melatonin concentration, core body temperature, and attentional performance were measured for each participant. Among the college student group, dynamic lighting had a markedly greater positive effect on alertness, circadian rhythms, and performance than constant lighting. In addition, intermittent lighting had a more substantial impact on core body temperature than constant or dynamic lighting. However, intermittent and dynamic lighting did not significantly differ in their effects on subjective alertness, melatonin secretion, or attentional performance. Furthermore, the positive effects of lighting on various indicators were most pronounced at 6:30-8:30, 8:30-10:30, and 19:30-21:30. The results confirmed that the effects of lighting on alertness and circadian rhythms were more significant during the morning and evening than at other times and that dynamic lighting had a more substantial effect than constant or no lighting. The study results offer a theoretical basis for human-centered indoor lighting design, thereby improving worker alertness and reducing incidents involving unsafe conditions.