Using circadian lighting, in which artificial lighting is synchronized with natural biological rhythms or a person’s “internal clock,” significantly improves the sleep quality and work performance of night shift workers, a large new study has found. The study is among the first rigorous laboratory experiments to simultaneously examine the effects of circadian lighting on markers of the internal clock, cognitive performance during the work shift and sleep after an abrupt transition to night shift work.

The results of the study were published in two articles in the Oxford University Press SLEEP journal. They conclude that strategic light exposure speeds up internal clock adjustment and improves alertness and performance as well as sleep after a night shift.

The Challenges of Night Shift Work

Circadian rhythms reflect our body’s internal clocks that control the activity and timing of bodily functions, including our sleep-wake cycle,” says Dr. Hannah Scott, a sleep researcher at Flinders University and author of Circadian-informed lighting improves vigilance, sleep, and subjective sleepiness during simulated night shift work. Shift work causes disruption of the circadian rhythm, for which well-timed light exposure, designed to promote wakefulness and facilitate circadian adjustment, is one of the most effective methods of resetting the body clock.

In Australia, approximately 15 to 16 percent of employees report being shift workers. For both men and women, rotating shifts with weekly changing schedules are the most common form of shift work. The results, supported by the Defence Science and Technology Group under the Research Network for Undersea Decision Superiority, are of particular interest to shift workers in enclosed spaces where lighting is typically dim.

Researchers wanted to examine the unique challenges that night shift work presents, particularly the disruption of sleep-wake cycles that can lead to impaired mental and physical performance, poorer sleep and health issues. They found that the use of circadian lighting improved work performance and sleep for individuals who work irregular shifts.

Circadian Lighting Can Improve Performance, Sleep, Safety and Well-Being for Night Shift Workers

The study involved 19 adults who were examined in the FHMRI’s Sleep Health Lab under tightly controlled conditions that simulated night shift working conditions. Participants were exposed to two different lighting scenarios over an eight-day period to compare how their internal clocks adjusted and how they performed on a range of tasks. The circadian lighting consisted of blue-enriched and dimmed light, light with reduced blue content, which was designed to support the adaptation of the internal clock to night work, while the traditional dimmed lighting, light with reduced blue content, simulated the standard lighting conditions on board submarines. The research team then evaluated important circadian measures, including melatonin levels and core body temperature, as well as other outcomes, including cognitive performance and sleep.

Importantly, circadian lighting advanced the participants’ body clocks by about an hour a day compared to standard lighting in four consecutive simulated night shifts. Alisha Guyett, lead author of “A circadian lighting intervention accelerates circadian adjustment to a night work schedule in a submarine lighting environment,” says the results are very promising for employers and employees on night shifts.

The overarching benefits of circadian-aligned lighting for sleep and wakefulness are clear from this study. The results suggest that strategic lighting interventions are likely to be used to improve the performance, sleep, safety, and well-being of night shift workers who are exposed to inadequate light during their work shift. This type of lighting significantly accelerated the participants’ adaptation to night work, which could have important implications for improving the health and performance of those who regularly work night shifts.

Specifically, participants achieved almost an hour more of sleep after circadian lighting compared to standard lighting conditions and reported less sleepiness during their shifts. To test attention, participants in both light conditions were given the Psychomotor Vigilance Task (PVT), a behavioral attention test. Participants in circadin-informed light conditions made half as many errors (7.4 slips) as participants in standard lighting (15.6 slips).

According to the researchers, this study underscores the importance of the circadian system and circadian-friendly lighting to alleviate some of the significant challenges of shift work. These findings have important implications for lighting conditions on submarines, as well as in mining and other work environments where lighting conditions may make it difficult for shift workers to successfully adjust their internal clocks to their work schedule.