Metrology for wearable light loggers and optical radiation dosimeters
The day-night cycle has always cadenced life in nature, even long before the advent of human society. While fire was already used to fight the dark of night, it is only recently that humans have started consistently and systematically lighting up their night life through the invention of electric lighting. But staying indoor under artificial light, especially LED light which vastly differs from sunlight, or staying up late at night in well-lit places, is not what the human body is used to. From sleep disruption and stress to physical and mental health issues, all sorts of negative and often related effects can come from inappropriate light exposure.
These effects are more and more studied and in 2018, the International Commission on Illumination (CIE) released the CIE S 026:2018 standard. This standard defines spectral sensitivity functions, quantities and metrics to describe the ability of optical radiation to stimulate each of the five eye photo-receptor types that can contribute, via the melanopsin-containing intrinsically-photosensitive retinal ganglion cells (ipRGCs), to retina-mediated non-visual effects of light in humans.
The study of the non-visual effects of light and the application of the CIE S 026:2018 standard need appropriate measurement tools, which come in the form of wearable light loggers. These sensors come in multiple forms, wearable positions, and use different technologies to provide metrics, often through different data methods. This lack of a harmonized framework for the characterisation and use of wearable light loggers is detrimental to data validation, comparison and reproducibility.
While UV dosimetry is already well established for artificial light sources in work environment, solar UV monitoring with portable radiometers suffers from a lack of framework for the characterisation of the dosimeters. It is nonetheless a major health concern with rising UV exposure for outdoor workers and the general public due to climate change, increasing cases of skin cancer.
Project MeLiDos proposes to bring such a framework with a consortium of European experts in the fields of metrology, chronobiology, lighting and light sensing. The project will work around three key thematic:
Harmonised characterisation methods for light loggers and solar UV dosimeters, with a focus on practicality and cost efficiency adapted to wearable devices.
Guidance on the use of wearable light loggers, from device selection to data representation, including data collection, validation and analysis, with a focus on making the data Findable, Accessible, Interoperable and Reproducible (FAIR).
Investigations on the necessity and benefits associated with using spatially-resolved light logging devices (e.g. image-based) in order to more closely represent light exposure in the retinal plane.
The project will run over three years, ending in May 2026. The results will be made available here and presented at several events throughout these three years. The MeLiDos Consortium welcomes any feedback or uptake of its results, interested parties can join the project as a stakeholder or access materials and results through our website, Zenodo storage space or by contacting any member of the Consortium.