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Abstract Light profoundly impacts many aspects of human physiology and behaviour, including the synchronization of the circadian clock, the production of melatonin, and cognition. These effects of light, termed the non-visual effects of light, have been primarily investigated in laboratory settings, where light intensity, spectrum and timing can be carefully controlled to draw associations with physiological outcomes of interest. Recently, the increasing availability of wearable light loggers has opened the possibility of studying personal light exposure in free-living conditions where people engage in activities of daily living, yielding findings associating aspects of light exposure and health outcomes, supporting the importance of adequate light exposure at appropriate times for human health. However, comprehensive protocols capturing environmental (e.g., geographical location, season, climate, photoperiod) and individual factors (e.g., culture, personal habits, behaviour, commute type, profession) contributing to the measured light exposure are currently lacking. Here, we present a protocol that combines smartphone-based experience sampling (experience sampling implementing Karolinska Sleepiness Scale, KSS ratings) and high-quality light exposure data collection at three body sites (near-corneal plane between the two eyes mounted on spectacle, neck-worn pendant/badge, and wrist-worn watch-like design) to capture daily factors related to individuals’ light exposure. We will implement the protocol in an international multi-centre study to investigate the environmental and socio-cultural factors influencing light exposure patterns in Germany, Ghana, Netherlands, Spain, Sweden, and Turkey (minimum n = 15, target n = 30 per site, minimum n = 90, target n = 180 across all sites). With the resulting dataset, lifestyle and context-specific factors that contribute to healthy light exposure will be identified. This information is essential in designing effective public health interventions.

The existence of a growing myopia pandemic is an unquestionable fact for health authorities around the world. Different possible causes have been put forward over the years, such as a possible genetic origin, the current excess of children’s close-up work compared to previous stages in history, insufficient natural light, or a multifactorial cause. Scientists are looking for different possible solutions to alleviate it, such as a reduction of time or a greater distance for children’s work, the use of drugs, optometric correction methods, surgical procedures, and spending more time outdoors. There is a growing number of articles suggesting insufficient natural light as a possible cause of the increasing levels of childhood myopia around the globe. Technological progress in the world of lighting is making it possible to have more monochromatic LED emission peaks, and because of this, it is possible to create spectral distributions of visible light that increasingly resemble natural light in the visible range. The possibility of creating indoor luminaires that emit throughout the visible spectrum from purple to infrared can now be a reality that could offer a new avenue of research to fight this pandemic.

Over recent years, a technological revolution has taken place in which conventional lighting has been replaced by light emitting diodes (LEDs). Some studies have shown the possibility that blue light from these artificial sources could have deleterious effects on the retina. Considering that people spend a non-negligible time in front of screens from computers and mobile phones, the eyes receive blue light of different intensities depending on the source. Nevertheless, any study about the visual and non-visual effects of blue light must consider precise measurements taken from actual artificial sources. For this reason, we have analyzed the spectral emission of 10 different electronic devices and weighted them according to the hazard caused by blue light to the eyes, comparing the results with solar radiation simulated with a radiative transfer model. The maximum spectral irradiance of the measured electronic devices at 10 cm from the detector was located between 440 nm and 460 nm. The irradiance for blue light hazard ranged from 0.008 to 0.230 Wm−2 depending on the particular characteristics of each electronic device. In contrast, the solar radiances in the same spectral range are larger both under clear and cloudy conditions.