Abstract
Laboratory experiments have been conducted by the Laboratoires des Ponts et Chaussees to investigate the conditions of motorists' night vision in heavy fog. These experiments, performed with stationary observers, yielded a quantitative evaluation of the contrast loss of three targets having different sizes and intrinsic luminances, and the thresholds of perception and identification of a message. While inter-individual differences cause large dispersions, the variations in mean threshold contrast are significant. These experiments also revealed the influence of the atmospheric veiling luminance created by the target, and of target dimensions on visibility.