Page 186 - AJWEP-22-6

Asian Journal of Water, Environment and Pollution. Vol. 22, No. 6 (2025), pp. 180-197.
doi: 10.36922/AJWEP025310242

ORIGINAL RESEARCH ARTICLE

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

study from Bulgaria

Plamen Tsankov * , Milko Yovchev 1,2 , and Hristo Ibrishimov 1,2
1,2
1 Department of Electric Power Distribution and Equipment, Faculty of Electrical Engineering and Electronics, Technical
University of Gabrovo, Gabrovo, Bulgaria
2 Laboratory Eco-friendly, Energy-saving, and Electromagnetically Compatible LED and Renewable Energy Components
and Technologies, Center of Competence “Intelligent Mechatronics, Eco- and Energy-Saving Systems and Technologies,”
Gabrovo, Bulgaria
*Corresponding author: Plamen Tsankov (plamen@tugab.bg)

Received: August 1, 2025; 1st revised: August 15, 2025; 2nd revised: August 18, 2025; Accepted: August 19, 2025;
Published online: September 11, 2025

Abstract: 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 He project involved a complete transition from outdated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.

Keywords: Light-emitting diode street lighting; Street lighting audit; Street lighting modeling and optimization;
Energy efficiency; Smart lighting control; Carbon dioxide emission reduction; Public lighting retrofit

Volume 22 Issue 6 (2025) 180 doi: 10.36922/AJWEP025310242