Abstract
Light is a variable of key interest in circadian rhythms research, commonly measured using wrist-worn sensors. The GENEActiv Original is a cost-effective and practical option for assessing light in ambulatory settings. With increasing research on health and well-being incorporating sleep and circadian factors, the validity of wearable devices for assessing light environments needs to be evaluated. In this study, we tested the accuracy of the GENEActiv Original devices (n = 10) for recording light under a range of ecologically relevant lighting conditions, including LED, fluorescent, infrared, and outdoor lighting. The GENEActiv output had a strong linear relationship with photopic illuminance. However, the devices consistently under-reported photopic illuminance, especially below 100 lux. Accuracy below 100 lux depended on the light source, with lower accuracy and higher variability under fluorescent lighting. The device’s accuracy was also tested using light sources of varying spectral composition, which indicated that the device tends to under-report photopic illuminance for green light sources and over-report for red light sources. Furthermore, measures of photopic illuminance were impacted by infrared light exposure. We conclude that the GENEActiv Original is suitable for mapping light patterns within an individual context, and can reasonably differentiate indoor vs. outdoor lighting, though the accuracy is variable at low light conditions. Given the human circadian system’s high sensitivity to light levels below 100 lux, if using the GENEActiv Original, we recommend also collecting light source data to better understand the impact on the circadian system, especially where participants spend prolonged periods in dim lighting.
Highlights
Light is the key zeitgeber responsible for synchronizing the circadian clock [1] and is a critical measure in studies assessing circadian outcomes
Linearity Test (LED and Fluorescent Light Sources) GENEActiv output in lux was compared to the gold-standard measure of photopic lux using a luxomGeEteNrEuAndcteivr tohuetspaumt einlilguhxtwcoansdciotimonpsa.rGedENtoEtAhectgivolsde-nsstoarnsdhaardd ma setarsounrgeloinfepahrorteolaptiiconlusxhiupswinigtha lluuxxommeeteterrreuanddienrgtshuensdamerebloigthhtflcuoonrdeistcieonnts.(rG=E0N.9E9A9,ctpiv< s0e.0n0s0o1rs) ahnadd La EstDrolnigghltinseoaurrcreelsa(trio=n0sh.9i9p9w, pit
While the device displays very high inter-device agreement and a strong linear relationship for high light intensities, it tended to under-report photopic illuminance below 100 lux, with the degree of inaccuracy depending on the type of light source
Summary
Light is the key zeitgeber (time cue) responsible for synchronizing the circadian clock [1] and is a critical measure in studies assessing circadian outcomes. The human circadian system is highly sensitive to light, with its dynamic range overlapping with typical indoor light levels [2,3], and peak sensitivity to blue light [4,5]. Accurate assessment of an individual’s light exposure profile, including under typical indoor lighting, is essential to understanding the impact of light on the circadian system. In field-based sleep and circadian studies, light exposure is currently widely measured using wrist-worn devices (e.g., [6–10]), due to their convenience and availability. GENEActiv devices are an affordable tool commonly used for this purpose, with 37 studies since 2014 having used the device’s light outputs (Google Scholar search terms “GENEActiv”+“light”+“lux” or “GENEActiv”+“light”+“lx”). An advantage compared to other actigraphic devices is the ability to use raw data with open-access tools developed for analysis and data visualization [11–14]
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