The effects of colour contrast and pavement aggregate type on road lighting performance

This paper focuses on studying the effects of colour contrast and pavement aggregate type on road lighting performance. Road lighting visibility experiments are conducted to study the visibility of achromatic and coloured targets in metal halide (MH) lamp and high pressure sodium (HPS) lamp road lighting installations. Pavement measurements are made to investigate the effects of aggregate lightness and aggregate colour on reflectance properties of pavements. Finally, the effects of vehicle windshields on driver's visibility and road lighting performance are discussed. The results of visibility experiments show that colours have a major effect on target visibility if the road is illuminated with a light source with adequate colour rendering properties. Thus in road lighting design it cannot always be assumed that targets on the road are achromatic and visible to the driver only because of the adequate luminance contrast. As expected, colours have more significant effect on target visibility when illuminated with MH lamps compared to HPS lamps. The results of pavement measurements show that aggregate colour and especially aggregate lightness have a significant effect on pavement reflection properties. For the most of the measured pavements the relative reflectances were higher for the long wavelength region of the visible spectrum. The pavement measurement results suggest that due to the higher content in the long wavelength region HPS lamps are more effective than MH lamps in terms of light reflected from the pavements. According to the results it can be concluded that road pavement is a very important parameter in optimisation and development of road lighting energy efficiency.