Energy-efficient light-emitting diode retrofit and advanced control in municipal street lighting: A case study from Bulgaria

Modernizing street lighting through light-emitting diode (LED) retrofits and advanced controls is recognized as an effective strategy for reducing energy use and costs. While numerous studies confirm these benefits in Western Europe, little is known about their performance in Eastern European municipalities. This study addresses this knowledge gap by presenting a case study of municipal street lighting in Bulgaria. It presents the methodology, implementation, and evaluation of an energy-efficient modernization project for municipal street lighting systems in the Bulgarian cities of Pavlikeni and Byala Cherkva. He project involved a complete transition from outdated lighting technologies (e.g., high-pressure sodium, compact fluorescent, and mercury vapor lamps) to high-efficiency LED luminaires, integrated with an intelligent control and monitoring system. An energy audit, conducted in accordance with national regulations and European standards (EN 13201), revealed that over 90% of luminaires had exceeded their operational lifespan and no longer complied with photometric and technical requirements. Lighting design classifications were applied in accordance with EN 13201:2016 to ensure compliance with the standard’s requirements for luminance, uniformity, and glare control. An optimization problem was defined and solved using specialized software to determine the lowest luminaire power, minimum pole height, and smallest bracket tilt angle, with fixed pole spacing, while maintaining regulatory compliance. Using DIALux evo, multi-scenario photometric simulations and optimizations were performed, resulting in 47 optimized lighting models tailored to specific street segments. The upgraded system incorporates adaptive dimming features, enabling nighttime power reduction through pre-programmed driver settings. A centralized cloud-based management system was implemented for remote monitoring and control, enhancing reliability and reducing maintenance. Post-implementation analysis demonstrated 79.5% energy savings (549,082 kWh/year), along with carbon dioxide emission reductions of 1,349 t/year and a financial payback period of 6.2 years. This case study highlights the technical, economic, and ecological viability of large-scale LED retrofit projects with smart controls, offering a replicable model for municipalities across Central and Eastern Europe seeking improved energy efficiency and reduced environmental impact.