Wearable devices for circadian lighting: Spectral, spatial, photometric, melanopic, and thermal performance of dosimeters

Light is one of the primary stimuli for the entrainment of human circadian rhythms and holds enormous potential in aiding precision medicine. Past laboratory studies conducted in controlled environments highlighted the importance of photic history, intensity, spectrum, and timing of light exposure. More recently, field studies have indicated that analyzing the real-world impact of lighting on human health can be complex due to confounding factors. When properly designed, field studies can provide insight into occupants’ daily light exposure and be linked to physiological and psychological outcomes. However, measuring daily light exposure requires an accurate, durable, and affordable wearable light dosimeter that can be attached to a participant. Here, the spectral, spatial, and thermal performance of three wearable dosimeters (LYS Buttons, Blue Iris Specks, and Actiwatch Spectrums) are investigated. Light measurements taken by dosimeters under various lighting conditions, along with melanopic and photometric calculations, were benchmarked against a calibrated spectroradiometer. The LYS Button was the easiest to use and operate, albeit with reduced photometric accuracy. The Blue Iris Speck had the highest photometric and data-logging accuracy. The Actiwatch had the poorest photometric performance, which raises caution for scientific use. Results can help product designers and engineers improve their products and help chronobiology and sleep researchers to develop experimental protocols to account for weaknesses and capitalize on the strength of dosimeters. Future studies should evaluate the updated versions of the available light dosimeters and compare the performance of the dosimeters based on the wearing position on the user body.