Analysis of exposure to ALAN (Artificial Light at Night) in the urban space of Madrid and Toledo (Spain) and its impact on human circadian rhythms: "circadian neurolighting"

This research explores the visual and non-visual (circadian) perception of light in humans and their brain responses in the urban spaces of two contrasted cities: Madrid and Toledo, in Spain. Lighting has been demonstrated to induce the synthesis of neurotransmitters, which can function as regulators or disruptors of our biological system, causing diseases due to the alteration in our circadian rhythms; these responses are contingent upon the technical properties of the lighting (type of incidence, intensity, colour temperature, and primarily, wavelength), as well as the time and duration of exposure. In Madrid, we analyse Gran Via, a iconic and busy avenue with high commercial and touristic activity. This has resulted in an excess of illumination, which has a notable impact on the night environment and, in particular, on the biology of the human beings who transit and inhabit these areas. In contrast to Toledo-a small, protected city (a UNESCO World heritage site since 1986) that has maintained a low population density, controlled commercial areas, and a low level of urban lighting at night-Madrid represents an opposite situation. In Madrid, measurements of both lux and light spectrum were taken to demonstrate the excessive light incidence, along with the high emission of short-wavelength light produced by LED screens, which, at night, disrupt our circadian cycle. This paper demonstrates how artificial light at night (ALAN) affects human circadian rhythms. Furthermore, this study suggests directions for urban lighting design, considering human circadian rhythms.