Optimisation of lighting quality and energy efficiency of LED luminaires in roadway lighting systems on different road surfaces

Abstract

Lighting quality plays an important role in determining the visual performance and visual comfort of the road user, which help keep driver alert. Lighting quality depends on various factors, such as mounting height, luminaire spacing, luminaires, overhang, boom angle, and road surface properties. The light that reflects from the road surface enters the eyes of the road user, and makes the road visible. However, prevailing conditions on the roadway determine the reflection properties of the road surface. This paper presents the analysis of lighting quality in different road surface conditions using the DIALux software. Dry and wet road surfaces are used to study lighting quality following the classifications of the International Commission on Illumination (CIE), where the lighting qualities of high-pressure sodium (HPS) and light-emitting diode (LED) luminaires are compared, based on a roadway without a traffic island. In addition, it presents the design of a roadway lighting system with optimised LED luminaires, by adjusting pole spacing and mounting height, ensuring the best installation in each classification of road surface. Thereafter, energy evaluations of different input powers of LED luminaires are discussed and compared with the HPS luminaire. Results indicate that the HPS luminaire can provide better average illuminance and average luminance values than LED luminaires, resulting in positive visual performance. However, LED luminaires can achieve better overall visual and comfort performances, including energy saving, due to their light distribution efficiency. For lighting quality in different road surface conditions, the wetter the road surface, the higher the lighting quality; because wet road surfaces cause alternating bright and dark areas on the road. This results in increased average luminance of the surface, and decreased longitudinal uniformity. Moreover, road surfaces with high average luminance coefficient, Q0, can accommodate larger pole spacing, reducing energy consumption. Using LED luminaires with lower or higher input power than the optimal power, however, result in higher energy consumption.