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 multisource model of discomfort glare. The practical implications are discussed.

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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 Hz).

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