Energy Efficiency of Road Lighting Without Specific Numerical Indicators

Energy efficiency in road lighting is increasingly critical for sustainable urban development, yet numerical indicators essential for objective evaluation are often misunderstood or misapplied. This paper addresses fundamental misconceptions in interpreting the Power Density Indicator (PDI), a key metric for assessing lighting system efficiency. Through analysis of Romanian street lighting modernization projects and extensive literature review, we demonstrate widespread misunderstanding of PDI’s properties, including inappropriate summation across streets and failure to recognize its independence from road class. We present a comprehensive methodology for PDI interpretation and optimization through spatial visualization of Luminous Intensity Distribution Curves (LIDCs) using MATLAB’s MESH function. The theoretical framework derives minimum achievable PDI values as a function of LED-specific efficacy and system utilance. Case studies from 181 streets in Romanian cities reveal significant optimization potential. Finally, we demonstrate, through computational simulation, the theoretical ideal: a perfectly adapted LIDC achieving unitary utilance, confirming that minimum PDI depends solely on LED efficacy and optical efficiency. These findings provide practical guidance for designers to optimize energy efficiency while meeting photometric requirements.