Photometric Monitoring of Luminous Street Furniture in Porto: 2024–2025 Evolution and Policy Implications

Abstract: Background - Advertising light sources (LED panels, MUPI, bus shelters) contribute to urban light pollution. In 2021, Porto, Portugal, municipal tender specifications set night-time thresholds of luminance (Lᵥ ≤ 100 cd·m⁻²) and correlated colour temperature (CCT ≤ 2200 K). We report compliance and change across three campaigns (2024–2025). Methods - Stratified night-time measurements were undertaken by typology and concessionaire, on a sample of the equipment. For each radiant face, mean and peak luminance were recorded with two calibrated instruments by three independent observers – targeting the brightest content for peaks –, plus illuminance (under selected shelters) and CCT. Results - campaign 1 (May 2024) showed low compliance despite prior specification provided to concessionaires (BrandExposure, DreamMedia, JCDecaux). Considering % mean, % peak luminance compliance, result was: (shelters) JCDecaux 60.0, 60.0; DreamMedia 0.0, 0.0; (MUPI) JCDecaux 100, 75.0, DreamMedia 25.0, 25.0; (LED panels) BrandExposure: 85.7, 42.9. By campaign 3 (July 2025) the picture improved: (shelters) JCDecaux 100, 100; DreamMedia 75.0, 50.0; (MUPI) DreamMedia 57.1, 25.0; (LED panels) (BrandExposure): 50.0, 0.0. Luminance trajectories show general improvement, with few exceptions. CCT generally exceeded 2200 K (except for some JCDecaux equipments) and has not suffered major corrections yet. Illuminance was not considered due to interference from streetlights. Conclusions - Gains in campaigns 2 and 3 suggest that an assess-implement-audit loop is effective. Persistent LED-panel breaches support the luminance control approach with content-based caps, night-time switch-off, and CCT≤2200 K. We recommend incorporating peak-based compliance and biannual audits into contracts. Photometric Monitoring of Luminous Street Furniture in Porto: 2024–2025 Evolution and Policy Implications DOI: Keywords: light pollution; led panels; light pollution policies; light pollution ordinances. Raul Cerveira Lima, Carmen Bao-Varela, Justo Arines 1,2 3 3 Escola Superior de Saúde, Instituto Politécnico do Porto, R. António Bernardino de Almeida, 4200-072 Porto, Portugal. Instituto de Astrofísica e Ciências do Espaço, Universidade de Coimbra, Coimbra, Portugal. IMATUS institute of Materials and Faculty of Óptica and Optometry, University of Santiago de Compostela, Spain 1 2 3 Night Sky Measurements and Astronomy Education 27 Corresponding Author: r[email protected].pt