The influence of façade colour, glazing area and geometric configuration of urban canyon on the spectral characteristics of daylight.

Since the non-image-forming (NIF) effect of daylight on the human circadian system is widely accepted, adequate exposure to daylight is now considered one of the elements of a healthy life. In urban environment, one of the prerequisites for adequately lit indoor spaces is the amount and quality of daylight reaching the window, which is highly dependent on the characteristics of the urban environment. The aim of the study was to determine whether there are correlations between urban density (i.e., distance between buildings, building height), façade surface characteristics (i.e., colour and Window-to-Wall Ratios – WWR) and NIF potential of daylight. The study was conducted on a parametric geometric model of a street canyon covering a wide range of characteristics. Simulation results were interpreted using the Relative Melanopic Efficacy coefficient and Sky View Factor. The results indicate that the colour of the opposite façade can substantially impact the resulting NIF potential, especially for orange-red or blue hues. The results of the study show that this influence for building heights between 3 and 8 storeys becomes significant when the width of the urban canyon is less than 25 m and becomes substantially smaller at WWRs above 30 %. • Parametric evaluation of daylight spectral composition and urban canyon properties. • Façade colour effect becomes significant at urban canyon height-to-width ratios ≥1. • NIF daylight potential in urban canyons is directly correlated to urban density. • Increasing the WWR reduces the impact of façade colour on NIF daylight potential. • Results underscore the importance of façade colour in urban design decisions. [ABSTRACT FROM AUTHOR]