Lighting the path forward: the value of sleep- and circadian-informed lighting interventions in shift work

Visible light exposure induces a broad spectrum of physiologic responses, ranging from changes in gene expression to overt behavior [1–4], which can impact health and well-being. While light has been used therapeutically since antiquity, the advent of modern solid-state lighting technology presents new possibilities to optimize lighting conditions in the built environment for better health.

The light–dark cycle is the primary synchronizer of the mammalian central circadian pacemaker [5–8]. Aberrant light exposure can misalign circadian rhythms, which are ~24-hour endogenously generated physiologic oscillations, relative to each other and relative to external social and work schedules. Circadian misalignment is pervasive in clinical (e.g. circadian rhythm sleep–wake disorders) and general populations (e.g. shiftworkers, jet lag). A majority of individuals working nonstandard hours, including shiftworkers, have aberrant light exposure and associated circadian rhythm misalignment and sleep disruption. Up to 30% of shiftworkers meet the diagnostic criteria for a shiftwork sleep disorder, marked by significant complaints of insomnia, excessive sleepiness, and functional impairments [9]. Chronic circadian misalignment and sleep disruption, such as in shiftwork are implicated in major health conditions, from depression to diabetes and an increased risk of errors, accidents, and injuries [10].

Optimized lighting can be an effective countermeasure for shiftwork-related adverse effects on health and safety. Controlling the key characteristics of light exposure, including the timing [11], intensity [12], duration [13] and spectrum [11] facilitates synchronization of the endogenous circadian pacemaker (Figure 1) to shifted sleep–wake and work schedules through robust phase resetting of the circadian pacemaker [14–16]. Additionally, visible light exposure has acute alerting effects, reduces sleepiness, improves mood, and neurobehavioral performance [1, 15, 17–19]. These improvements translate to improved safety and productivity [20–24].

Figure 1.

Nonstandard work hours, such as in-shift work is one of the most common causes of circadian misalignment. Sleep- and circadian-informed lighting solutions are effective but underutilized in shiftwork management. When optimized for circadian adaptation, short-wavelength enriched light can suppress melatonin, induce alertness, and induce robust phase resetting. Although there is a monotonic relationship between duration and intensity with and non-visual responses (e.g. melatonin suppression, phase resetting, and alertness), the relationship is typically nonlinear such that even short duration and moderate intensity exposures can induce larger than expected responses compared to longer duration high-intensity exposures. Guyett, Scott, and colleagues tested the use of moderate-intensity, short-wavelength enriched, longer-duration light exposure to improve circadian adaptation, sleep, and neurobehavioral performance in the context of submariner work. Optimization of lighting depends on individual differences, organizational requirements, and work environments. To enable widespread adoption and implementation, we require larger studies testing the effectiveness and documenting return on investment. Further work must consider tailoring light interventions to address individual variability and ensure scalability through integration with other health and wellness initiatives.

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Guyett and colleagues [25] evaluated the impact of ambient lighting optimized for shiftwork based on sleep and circadian principles on circadian phase resetting in a controlled laboratory setting. In an 8-day protocol, healthy, shift-work naïve individuals followed a simulated “submariner schedule” that included daytime sleep between 10:00 and 19:00 hours and overnight simulated work between midnight and 8:00 hours. In a 2-visit randomized crossover design, participants were exposed to either standard or optimized lighting. The timing, intensity, and duration of light exposure were optimized for circadian phase delays using the model of arousal dynamics [26, 27]. The sleep- and circadian-informed lighting paradigm consisted of a gradual transition to moderately bright, short-wavelength (blue) enriched light (wall-mounted LED lights, melanopic-EDI 238 lux [430 lux]), then to dim, short-wavelength depleted lighting (melanopic-EDI 3 lux [7 lux]) at group-average time of the core temperature minimum. Light timings were adjusted daily based on predicted phase delays. The optimized lighting schedule resulted in a ~1.5 hour per day delay shift of the central pacemaker, as measured using the gold-standard phase marker dim light melatonin onset (~6.5-hour total shift, ~50% of the target 12-hour shift in the work schedule). Scott and colleagues [28] extended these findings, documenting a 52-minute increase in the total sleep time, a 9% improvement in sleep efficiency, and marginal improvements in psychomotor performance.

These phase resetting results are consistent with previous studies in other simulated work schedules and conditions, such as space missions [29–31]. The neurobehavioral results align with other studies documenting that short-wavelength enriched light exposure during overnight shifts enhances alertness and operational performance in various environments [20, 23, 32–35], underscoring the positive impact of visible light in overall adaptation to shift work.

Despite accumulating evidence, the adoption of circadian-informed lighting in shift-work industries remains limited. This is likely precipitated by the paucity of value proposition evaluations [36, 37], partly due to limited sample sizes in research studies that often preclude generalizability. While targeted studies provide the essential proof-of-concept across diverse operational contexts, large-scale studies enabling generalization and assessing effectiveness are warranted. Evaluation of returns on investment across different operational settings is also limited [37–39], impeding institutional adoption. Research outcomes, such as phase shifts or improved cognitive performance are promising, but their translation to industry-specific key performance indicators is not readily clear, which minimizes enthusiasm and organizational buy-in for such technologies. Example performance indicators from an industry perspective may include operational readiness in defense; sick leave, inpatient stay duration in health care; reduced errors, and accidents in mining etc.

Figure 1 While emerging evidence strongly supports the implementation of sleep- and circadian-informed lighting (“SCHIL”) interventions, it is important to recognize that optimization is highly context-specific and not a “one-size fits all” approach [40]. Complete adaptation may be feasible and useful for submariners, where shifts follow a relatively stable pattern, but may be impractical for rapidly rotating shiftwork rosters, including healthcare, transportation, and service industries. Many of these workers may work multiple jobs, exchange shifts, or have changing work environments, which can lead to inconsistent light exposure schedules. In cases where continuous exposure may not be possible, workers may still benefit from bursts or brief pulses of light exposure to promote circadian adaptation [11, 31], or even partial adaptation (i.e. shifting melatonin peak into the first half of the daytime sleep episode) [41]. In other settings where circadian adaptation is not practical or possible, other lighting interventions aimed at acute alertness or fatigue mitigation may be the most feasible solution [23, 32, 42].

In addition to context-specific lighting interventions, personalized therapies are becoming increasingly vital, recognized as a strategic goal in sleep medicine [43]. There are extensive interindividual differences in sensitivity to light and non-visual responses to light exposure, including melatonin suppression, circadian resetting, and acute alerting effects [7, 44–49]. Personalized interventions that account for individual differences in circadian physiology, personal needs, operational circumstances, and schedules are more likely to succeed long-term [50–52] and reduce the need for extensive workplace lighting modifications [32].

Personalized lighting can integrate with other lifestyle, health, and wellness initiatives, making interventions more scalable and adaptable across industries. The model of arousal dynamics, which informed the circadian lighting solution in Guyett, Scott, and colleagues’ research [25, 28] has been used for delivering tailored sleep timing recommendations [53, 54], providing opportunities for much-needed multicomponent support for shift workers [55]. Personalized interventions can empower individuals to make informed choices, which may improve their engagement and overall implementation of such interventions.

Emerging evidence also indicates that while light exposure is the main time cue for setting the central pacemaker, non-photic stimuli such as meals may be the main time cue for resetting peripheral circadian rhythms [56–59]. Given that the goal is to reduce system-wide (i.e. whole animal) circadian disruption, future work needs to examine the interaction and optimization of both photic and non-photic cues to achieve comprehensive circadian adaptation and improvements in overall health.

Conclusion

Sleep- and circadian-informed lighting schedules are minimally intrusive, cost-effective, and scalable, especially in restrictive environments. The science of SCHIL interventions promoting circadian adaptation and improving neurocognitive performance is growing in robustness, with newer studies [25, 28] extending the wealth of evidence. Going forward, the value proposition and personalization of such interventions need to be carefully approached for their adoption and success in workplaces.

Disclosure Statement

Financial disclosures: PV and SAR have no financial disclosures related to the present editorial. SAR was supported in part by NIH-NHLBI R01HL159207, R01HL162102. Nonfinancial disclosures: PV holds patent for (1) Systems and methods for monitoring and control of sleep patterns (International Application No. PCT/AU2021/050126); through Monash University’s Entrepreneurship program, PV has explored the development of a digitalized sleep support for shift workers. SAR holds patents for (1) Method and device for preventing alterations in circadian rhythm (U.S. patent application Ser. No. 10/525,958), and (2) Methods and devices for improving sleep performance in patient exposed to light at night (U.S. Application No. 61/810,985); SAR owns equity in Melcort Inc.; has provided paid consulting services to Sultan & Knight Limited, Bambu Vault LLC, Lucidity Lighting Inc.; and has received honoraria as an invited speaker and travel funds from Starry Skies Lake Superior, University of Minnesota Medical School, PennWell Corp., and Seoul Semiconductor Co. Ltd., FALK FOUNDATION E.V.; SAR has received grant/research support from Seoul Semiconductor Co. Ltd., Biological Innovation and Optimization Systems, LLC, Merck & Co., Inc., Pfizer Inc., Vanda Pharmaceuticals Inc., Lighting Science Group, NIH, and NASA. These interests were reviewed and managed by Brigham and Women’s Hospital and Mass General Brigham in accordance with their conflicts-of-interest policies.

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