# Wearable Light-and-Motion Datalogers for Sleep/Wake Research: A Review
###### Abstract  
Long-term recording of a person's activity (actimetry or actigraphy) using devices typically worn on the wrist is increasingly applied in sleep/wake, chronobiological, and clinical research to estimate parameters of sleep and sleep-wake cycles. With the recognition of the importance of light in influencing these parameters and with the development of technological capabilities, light sensors have been introduced into devices to correlate physiological and environmental changes. Over the past two decades, many such new devices have appeared from different manufacturers. One of the aims of this review is to help researchers and clinicians choose the data logger that best fits their research goals. Seventeen currently available light-and-motion recorders entered the analysis. They were reviewed for appearance, dimensions, weight, mounting, battery, sensors, features, communication interface, and software. We found that all devices differed from each other in several features. In particular, six devices are equipped with a light sensor that can measure blue light. It is noteworthy that blue light most profoundly influences the physiology and behavior of mammals. As the wearables market is growing rapidly, this review helps guide future developments and needs to be updated every few years.  
human; actimetry; motion; ambient light +
Footnote †: journal: Medical Physics Letters  
0000-0001-999-22000-0000-0000-0000-0000-0000-0000-00000-0000-00000-0000-00  
sleep misperception, narcolepsy [2], and also some disorders beyond sleep domain such as movement disorders [3; 4] and epilepsy [5]. Wrist-worn actinetry is widely used in human chronobiological research.  
With growing evidence of the influence of ambient light on human physiology and behavior (e.g., [6; 7]) and to meet the requirements of many investigators, actineters became additionally equipped with light sensors that capture photons in the visible part of the electromagnetic spectrum. The gathered light exposure data are not only useful for correlating the dynamics of light and activity but also for a better distinction of episodes of time spent indoors and outdoors, with sleep and without sleep, wearing and not wearing a device. The first devices having both an accelerometer and light sensor appeared in the late 1990s. For example, the Activatch-L (invented by Cambridge Neurotechnology, Fenstanton, Cambridgeshire, UK, marketed together with Minimitter, Bend, OR, USA, with the subsequent sale of the trade rights to Philips Respironics, Bend, OR, USA) was launched in \(\sim\)1998 [8]. Furthermore, with the discovery of melanopsin-based photoreception in the eye in 2000, which mediates a variety of physiological reactions to light [9], an importance emerged to measure specifically blue light as these photoreceptors are sensitive to the light wavelength \(\sim\)480 nm [10]. Several existing light-and-motion dataloggers already provide such an opportunity.  
To our knowledge, many investigators wonder which datalogger is best for their research. The family of research-grade stand-alone devices has been expanded over the past two decades, and an abundant amount of consumer-grade smart devices have been developed in recent years to track activity or light. The present study is aimed at reviewing existing dataloggers that simultaneously measure human activity and ambient light for their basic differentiating characteristics--appearance, dimensions, weight, mounting, battery, sensors, features, communication interface, and software.