STUDY OBJECTIVES: Shiftwork is associated with cognitive impairment and reduced sleep time and quality, largely due to circadian misalignment. This study tested if circadian-informed lighting could improve cognitive performance and sleep during simulated night shifts versus dim control lighting.
METHODS: Nineteen healthy participants (mean ± SD 29 ± 10 years, 12 males, 7 females) were recruited to a laboratory study consisting of two counterbalanced 8-day lighting conditions (order randomized) 1-month apart: (1) control lighting condition - dim, blue-depleted and (2) circadian-informed lighting condition - blue-enriched and blue-depleted where appropriate. Participants underwent an adaptation night (22:00-07:00 hours), then four nights of simulated night work (cognitive testing battery of nine tasks, 00:00-08:00 hours), and sleep during the day (10:00-19:00 hours). Psychomotor vigilance task (PVT) lapses, Karolinska Sleepiness Scale (KSS) scores, and polysomnography-derived sleep outcomes were compared between conditions and across days using mixed models.
RESULTS: Significant condition-by-day-by-time of task interaction effects were found for PVT lapses, median reaction time, and reaction speed, with ~50% fewer lapses by the end of simulated shift work with circadian-informed lighting versus control (mean ± SD 7.4 ± 5.0 vs. 15.6 ± 6.1). KSS was lower around the night shift midpoints on days 6 and 7 with circadian versus control lighting. Participants slept 52 minutes longer [95% CIs: 27.5, 76.5 minutes] by day 7 with circadian-informed versus control lighting, p < .001. Effects were inconsistent on other performance tasks.
CONCLUSIONS: Circadian-informed lighting improved sleep, sleepiness, and vigilance compared to control lighting. These findings support the potential for lighting interventions to improve sleep and vigilance in night shift workers chronically exposed to dim lighting.
