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To limit glare, lighting engineers need to estimate the level of discomfort produced by a lighting installation. Outdoor, most discomfort glare models predict a mean level of discomfort on a judgment scale, which corresponds to a "mean road user." However, in real life, the inter-individual variability of the sensitivity to glare is large; predicting the mean discomfort does not describe the full pattern of responses in a population. We propose a methodology to model the Discomfort Level, computing the probabilities that an observer reports any of the levels of a discomfort scale. This methodology is demonstrated for outdoor lighting, where no probabilistic model is available. Using a dedicated psychophysical experiment, we extend the results of a previous study where a formula was proposed to compute the Glare Excitation due to a multi-source stimulus, at the Borderline between Comfort and Discomfort (BCD), with a background luminance consistent with outdoor lighting. This formula is first extended to other discomfort levels and background luminance levels, and strengthened thanks to a different experimental protocol and to the use of up to 10 glare sources simultaneously. From this experiment, a formula of the Glare Excitation is proposed in the range of outdoor lighting. Then, a probabilistic model of the Discomfort Level is proposed, allowing computing the probability of ratings at each level of an ordinal scale from the Glare Excitation computed with our formula. It is hoped that the proposed model avoids most of the modeling methodological caveats of previous discomfort glare models. [ABSTRACT FROM AUTHOR]

Many models of discomfort glare have been proposed for outdoor lighting applications. Most of them were built from data collected in the laboratory in static situations, with motionless light sources, which main characteristics (luminance, size and position) were constant over time. However, on the road at night, drivers are moving with multiple sources around them. To fill the gap between static situations and more realistic ones, four psychophysic experiments were carried out in a laboratory to investigate the impact of the cyclic variations of several light source characteristics (its luminance, eccentricity and solid angle) on the discomfort glare. The temporal frequencies have been chosen representative of outdoor lighting conditions, up to 2.6 Hz. No impact of the dynamics of the glare source was found, except for a source with variable luminance at a low frequency ( f = 0.65 H z). [ABSTRACT FROM AUTHOR]

The use of visual performance models in road lighting is an old idea: it was first proposed in the 1930s by Waldram with the Revealing Power, and by Roper and Howard who used the notion of visibility distance. The Visibility Level (VL) concept was then proposed by Blackwell, and the Relative Visual Performance by Rea and Ouelette. At the turn of the 21th century, some standards have considered using the VL in order to rate lighting installations through the Small Target Visibility concept. However, the use of visual performance indexes in lighting standards was recently withdrawed, which raises a question: what happened? [ABSTRACT FROM AUTHOR]

Many models have been developed to predict the discomfort glare generated by one light source in the visual field. Some of them were generalized to predict discomfort glare from several sources, but they were not directly built from multi-source data. In their generalization, they do not consider the potential interactions due to the fact that the light sources are switched on together. In the present work, a psycho-visual experiment was conducted for a better understanding of the glare produced by several sources using a matching task at the Borderline between Comfort and Discomfort (BCD). A formula is proposed to compute the photometric and geometric characteristics of an equivalent source which generates the same level of discomfort glare as several sources switched on together. This formula is the first step towards a multi-source model of discomfort glare. The practical implications are discussed. [ABSTRACT FROM AUTHOR]