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An asymmetric road lighting concept known as Probeam is investigated in this study for energy efficiency, contrast and visibility of vertical objects and road markings in highway lighting. Calculations based on road lighting standards, road surface and markings reflection characteristics and typical Dutch highway geometry, reveal that Probeam lighting improves the average visibility of objects and road markings over symmetrical lighting, however, with a 14% increase in luminous flux as per current road lighting standards. This increase in luminous flux is attributed to the symmetrical lighting's advantage in specular road surface reflection, leading to a reduction in the Counterbeam lobe size in the light intensity distribution when designed to meet the current road luminance requirement. Notably, by designing the Probeam luminaire to match symmetrical lighting's average visibility of vertical objects, for removing the road luminance requirement and dimming the luminaire, energy consumption is reduced by 52%. Halving the Probeam luminaire's mounting height leads to an impressive 82% energy savings. The study highlights the possibility of a balance in energy use and road safety using the Probeam concept, considering advancements in road luminaires and retroreflective materials. Due to glare, the relevance of the proposed Probeam concept is restricted to one-directional traffic on highways. [ABSTRACT FROM AUTHOR]

To drive safely and comfortably, an adequate contrast between the road surface and road markings is needed. This contrast can be improved by using optimized road illumination designs and luminaires with dedicated luminous intensity distributions, taking advantage of the (retro)reflective characteristics of the road surface and road markings. Since little is known about road markings' (retro)reflective characteristics for the incident and viewing angles relevant for street luminaires, bidirectional reflectance distribution function (BRDF)-values of some retroreflective materials are measured for a wide range of illumination and viewing angles using a luminance camera in a commercial near-field goniophotometer setup. The experimental data are fitted to a new and optimized "RetroPhong" model, which shows good agreement with the data [root mean squared error ( R M S E )<0.13, normalized root mean squared error ( N R M S E )<0.04, and the normalized cross correlation ratio ( N C C )>0.8]. The RetroPhong model is benchmarked with other relevant (retro)reflective BRDF models, and the results suggest that the RetroPhong model is most suitable for the current set of samples and measurement conditions.

Brightness is one of the most important perceptual correlates of color appearance models (CAMs) when self-luminous stimuli are targeted. However, the vast majority of existing CAMs adopt the presence of a uniform background surrounding the stimulus, which severely limits their practical application in lighting. In this paper, a study on the brightness perception of a neutral circular stimulus surrounded by a non-uniform background consisting of a neutral ring-shaped luminous area and a dark surround is presented. The ring-shaped luminous area is presented with 3 thicknesses (0.33 cm, 0.67 cm and 1.00 cm), at 4 angular distances to the edge of the central stimulus (1.2°, 6.4°, 11.3° and 16.1°) and at 3 luminance levels (90 cd/m 2 , 335 cd/m 2 , 1200 cd/m 2 ). In line with the literature, the results of the visual matching experiments show that the perceived brightness decreases in presence of a ring and the effect is maximal at the highest luminance of the ring, for the largest thickness and at the closest distance. Based on the observed results, an image-based model inspired by the physiology of the retina is proposed. The model includes the calculation of cone-fundamental weighted spectral radiance, scattering in the eye, cone compression and receptive field post-receptor organization. The wide receptive field assures an adaptive shift determined by both the adaptation to the stimulus and to the background. It is shown that the model performs well in predicting the matching experiments, including the impact of the thickness, the distance and the intensity of the ring, showing its potential to become the basic framework of a Lighting Appearance Model.