0353 Shining Light on Photic Measurement for Sleep and Circadian Field Studies

Abstract Introduction Light is the most potent signal for the circadian regulation of sleep. To quantify light’s biological impact via melanopic Equivalent Daylight Illuminance (EDI), photic intensity is weighted based on the spectral sensitivity of melanopsin. This metric for light and time-of-day specific threshold recommendations support development, standardization, and replication of studies of the physiological effects of light. Light measurement outside the lab poses many unique challenges (e.g. greater variability in timing, intensity, spectrum; individual factors; technology limitations). Thus, consistent methods for measurement and reporting are important for maximizing the utility of emerging tools. Methods A framework for assessing and reporting light in field studies was developed, incorporating: 1) factors that influence light exposure, 2) methods for capturing the most significant factors, 3) strategies for addressing unique tradeoffs and challenges, and 4) an initial step-by-step protocol for measuring and reporting lighting characteristics in field studies of the physiological effects of light. This framework was applied in multiple study protocols to inform development and refinement. Results All studies used both static and continuous measures, along with subjective assessments. In one study, lighting was not homogenous and therefore position and location in the space mattered (melanopic EDI seated vs standing, 133.84 vs 221.91 lux; between workstations (seated), 133.84 vs 62.29 lux). In a second study, lighting was more homogenous but varied by time-on-shift; thus, continuous measures with a stationary meter were used. In a third study, subjective assessment of behaviors that influence photic exposure patterns over the past month indicated individuals likely did not meet nighttime light recommendations (melanopic EDI < 1 lux): 73% used their phone in bed often or always before sleep; and 20% often or always checked their phone if awakened from sleep. Conclusion When measuring and reporting light in the field, a one-size-fits-all approach is impossible, but some level of standardization is necessary. The proposed multi-level framework expands on recent lab-based guidelines by making adaptations for field studies, facilitating the evidence-based translation of our fundamental understanding of the effects of light on sleep and circadian health. Support (if any) CDMRP JPC-5 Fatigue Countermeasures Working Group (#66619).