Measurement of Vertical Dispersion and Pollution Impact of Artificial Light at Night in Urban Environment

Excessive artificial light disrupts our lives and poses health risks. In mixed-use urban areas, commercial lighting conflicts with residential activities. Vertical towers exacerbate the issue, as lower-level lighting affects higher-level occupants, and more research is needed to understand the vertical dispersion of light and its impact on sleep disturbance. This work offers a simple mathematical model for height dependence of illuminance in an urban building. It correlates basic measurements to reduce the values of the Exponent (n) and Linear (Coeff2) coefficients in a standard power-law curve. The collection of only a few data points can help to investigate the extent of the lighting spread at various floors of the building. Even with the complex lighting environment in Hong Kong, the methodology is exercised in 8 sample buildings from 4 different neighbourhoods to show the insights from the testing results. The heights of the studied buildings range from 3 to 18 stories, and they are for residential and mixed use. While the average measured illuminance at the street level was between 37 lx and 303 lx for the 4 neighbourhoods, the average illuminance across building heights was 14 lx to 247 lx. The existence of multiple light sources on building facades disrupts the simple inverse-square relationship with a single light source. The power n values range from approximately-1.7 to-0.8, while the Coeff2 values range from 61 to 7603 for the measured buildings. These variations indicate deviations from the assumption of a single source and suggest higher luminance and the presence of light sources at higher heights. With the simple inverse-square relationship, the proposed methodology can help to determine the height where the recommended limit can be met given the light situation at the street level.