PROJECT SUMMARY / ABSTRACT Light is the strongest biological signal influencing the human circadian system, and by extension, sleep. Exposure to light of sufficiently high levels during the daytime, combined with dim light/darkness during the evening and night, is necessary to maintain robust and appropriately timed circadian rhythms in physiology and neuroendocrine secretion, and to promote good sleep of sufficient duration. Conversely, reduced light exposure levels throughout the daytime and increased light exposure occurring at the “wrong time” (e.g., the biological night) can disturb sleep by causing circadian misalignment, disrupting melatonin secretion, increasing neurocognitive arousal, delaying sleep initiation, and worsening sleep quality. The light environment and its impact on sleep is important to consider because sleep influences nearly all aspects of physical and mental health and disease, as well as daily function and performance. Thus, personal light exposure represents an important malleable contextual factor that influences a critical health behavior (sleep). In an ongoing prospective 3-year observational cohort study (R01HL146911, MPI: Chang/Shechter; “IMPROVE Study”), we are evaluating the impact of environmental stressors and disturbed sleep on cardiovascular and psychological risk in emergency department (ED) healthcare workers (HCWs). An overarching goal of the IMPROVE Study is to evaluate the short- and long-term contribution of objectively- estimated short sleep duration and poor quality sleep to acute and progressive changes in blood pressure and psychological risk (e.g., burnout). In the current administrative supplement, we will leverage the infrastructure of the ongoing IMPROVE Study to add on an objective assessment of personal light exposure patterns via a small wearable mini-spectrophotometer (light pin) in a subset of participants who are enrolled in the parent IMPROVE study. This subset of participants will wear the light pin during one of their scheduled annual 2- week data bursts in which sleep is continuously tracked under free-living conditions. The aim of the administrative supplement is to determine the relationship between light exposure patterns and our main behavioral predictor of cardiovascular and psychological risk—sleep. Examining how personal light exposure patterns relate to sleep will provide information on the mechanistic role of this factor in influencing sleep. This work can inform the development of novel behavioral interventions focusing on personal light exposure patterns to improve sleep and downstream health-related outcomes.

PROJECT NARRATIVE Sleep is one of the crucial behavioral and physiologic determinants of health and wellness, and is influenced by many internal and external factors such as underlying diseases, societal/work demands, socioeconomic factors, or environment. Light exposure is the strongest biological signal that influences the human circadian system, and by extension, sleep. The aim of this study is to examine the relationship between personal light exposure patterns and sleep duration and quality under real-life conditions.