Quantification of light exposure characteristics modulating non-visual responses with light-dosimetry

(1) Background: Extensive laboratory research has shown that physiological and behavioural responses to light are modulated by different light exposure characteristics, that is, spectral composition, intensity, duration, timing, temporal dynamics, prior history, and spatial distribution. However, it is unclear to what extent these laboratory-derived relationships generalise to complex real-world personal light exposure (PLE). To provide a basis for addressing this question, we conducted a comprehensive review of previously published dosimetry studies to identify methods and metrics for quantifying light exposure pattern characteristics. Since no dosimetry study has been found that quantified spatial distribution in PLE, we additionally conducted an exploratory pilot study of spatiotemporal dynamics of PLE to assess the potential relevance of spatial distribution of light in real-life. (2) Methods: In the pilot study, person-bound exposure time-series of melanopic radiance distribution and spectral irradiance were collected in different every-day environments. Measurements were collected using a novel setup, consisting of wide-angle video-photometers and spectrally resolved dosimeters worn at the chest and the forehead. Light distribution was measured at a high temporal resolution, with an epoch of 2 seconds at the chest and 10 seconds at chest and forehead. (3) Results: Analyses of the spatially resolved measurements show that spatial variability across the visual field can differ substantially between different everyday environments and contexts: spatial variability tended to be higher in indoor environments and environments dominated by electric lighting, and spatiotemporal variability was generally higher for measurements at the forehead than at the chest. Furthermore, hypothetical modelling of retinal spatial sensitivity suggests that the impact of spatial distribution on non-visual responses may strongly depend on the context and is likely to be small. (4) Conclusions: The pilot study is the first to provide spatially resolved measurements of PLE, showing that it is possible to quantify spatial distribution in dosimetry. The collected data may enable many interesting opportunities to examine and model retinal spatial sensitivity at the level of individual ganglion cells up to quantifying the effective light stimulus for non-visual responses. Finally, this study complements our comprehensive review, which provides a wide range of metrics to quantify different light exposure pattern characteristics. Taken together, these efforts form a basis towards a consensus framework for light-dosimetry studies and ultimately contribute to fostering the efficacy of research in real-life to answer pressing questions in many applied contexts, be it architecture, shift-work, or personal lifestyle.