Assessing the eco-centric light field to capture the light trespass of outdoor lighting

Abstract

Outdoor lighting supports human safety and visibility but also contributes to light pollution, which may disrupt ecological systems. This study applies an eco-centric lighting perspective, investigating the integration of three complementary lighting measurement methods using cubic light field measurements, vertical and horizontal illuminance, and luminance mapping. Three luminaire configurations, a conventional 4000 K road luminaire and two 2200 K alternatives (with and without louvre), were examined under varying environmental conditions (clear, cloudy, snowy clear and snowy cloudy). Measurements were conducted along a transect extending from the road into the adjacent terrain. Our findings demonstrate that, when combined, the three measurement methods capture both the spatio-directional spread and diffuseness qualities on the pavement together with the distal effects of the lighting. Horizontal and vertical illuminance measurements revealed that the alternative luminaires reduced spill light into the terrain by up to 45 % compared to the conventional luminaire, with a further 16.6–19.5 % reduction achieved using a louvre. Cubic light field measurements quantified the spatial characteristics of light, showing that light vector magnitude declined rapidly within 3–4 m from the luminaire, and diffuseness drastically changed under snowy conditions with an increase of 112 %. Luminance mapping illustrated differences in contrast and relative visibility between luminaire types; overall, the conventional luminaire tended to stand out more against the background sky. This integrative approach enables a more nuanced understanding of how artificial lighting interacts with the surroundings and may contribute to the development of more eco-centric lighting strategies.