Analysis of Exposure to ALAN (Artificial Light at Night) in the Urban Public Space of Madrid and Toledo (Spain) and Its Impact on Human Circadian Rhythms. Development of a New Concept: “Circadian Neurolighting”

This research explores visual and non-visual (circadian) perception of light on humans and their brain responses in the urban space 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 alteration of our circadian rhythms; these responses are contingent upon the technical properties of the lighting (type of incidence, intensity, colour temperature and mostly wavelength) and the time and duration of exposure. In Madrid, we analyse Gran Vía, an iconic and busy avenue with high commercial and touristic activity. This has resulted in an excess of illumination, that has a notable impact on the night environment and, in particular, on the biology of the human beings who transit and inhabit these areas. Unlike Toledo, a small, protected city (a UNESCO World heritage site since 1986) that has remained with a low population density, controlled commercial areas and a low level of urban lighting at night, is presented as 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 ALAN affects the human circadian rhythms. Furthermore, this research suggests directions for urban lighting design, considering the human circadian rhythms.