Associations between light exposure and sleep timing and sleepiness while awake in a sample of UK adults in everyday life

Abstract

Experimental and interventional studies show that light can regulate sleep timing and sleepiness while awake by setting the phase of circadian rhythms and supporting alertness. The extent to which differences in light exposure explain variations in sleep and sleepiness within and between individuals in everyday life remains less clear. Here, we establish a method to address this deficit, incorporating an open-source wearable wrist-worn light logger (SpectraWear) and smartphone-based online data collection. We use it to simultaneously record longitudinal light exposure (in melanopic equivalent daylight illuminance), sleep timing, and subjective alertness over seven days in a convenience sample of 59 UK adults without externally imposed circadian challenge (e.g., shift work or jetlag). Participants reliably had strong daily rhythms in light exposure but frequently were exposed to less light during the daytime and more light in pre-bedtime and sleep episodes than recommended [T. M. Brown et al. , PLoS Biol. 20 , e3001571 (2022)]. Prior light exposure over several hours was associated with lower subjective sleepiness with, in particular, brighter light in the late sleep episode and after wake linked to reduced early morning sleepiness (sleep inertia). Higher pre-bedtime light exposure was associated with longer sleep onset latency. Early sleep timing was correlated with more reproducible and robust daily patterns of light exposure and higher daytime/lower night-time light exposure. Our study establishes a method for collecting longitudinal sleep and health/performance data in everyday life and provides evidence of associations between light exposure and important determinants of sleep health and performance.

Power analysis for personal light exposure measurements and interventions

“…Another limitation of the demonstrated procedure is that it only applies to changes in metrics or (with slight adjustments) distributions of metrics, derived by from light exposure measurement. Many studies connect light exposure (and derived metrics) to other quantities or constructs, like sleep, alertness or mental health [11,13,14], and those other quantities will not be available in most datasets. A more theoretical approach for power estimation will be required there, such as described by Kumle, et al [24].…”

“…Developments in the eld of miniaturized sensor platforms have reduced the cost and size of these devices, while computational power and interfaces improved. We see a surge in studies using wearable light sensors in recent years, which is likely fueled by these developments in combination with increasing interest from the scienti c community [1,[11][12][13][14][15][16]]. This trend is likely to continue and bring new challenges for researchers working on the non-visual effects of light.…”

Recommendations for measuring and standardizing light for laboratory mammals to improve welfare and reproducibility in animal research

“…A simple design could integrate a spectrophotometer with suitable data processing capacity. Alternatively, cheap multichannel light sensors, which are increasingly being applied to measure human α-opic irradiances [ 47 – 49 ], could be recalibrated to measure species-specific metrics [ 46 ]. Examples of commercially available light meters and spectrophotometers are provided in S2 Table .…”

Protocol for a prospective, multicentre, cross-sectional cohort study to assess personal light exposure

“…These metrics can subsequently be linked to health outcomes of interest (Spitschan et al, 2022). For example, field studies using wrist-worn light loggers have shown an association between greater light exposure before sleep with lower self-reported alertness during the day (Didikoglu et al, 2023), poorer objective sleep quality (Cain et al, 2020), differences in sleep-wake consolidaton (Lok et al, 2023), and altered sleep architecture (Wams et al, 2017). Furthermore, higher light exposure during sleep has been linked to later sleep offset and poorer sleep continuity (Mead et al, 2023).…”