Abstract
In the current draft proposal of the European standard for variable message signs (VMS), the contrast between a symbol and its background (also called the luminance ratio) is an important parameter to describe the visual performance (VMS Standard, 1993). However, this parameter is tested in the laboratory at a relatively short distance, and hence, does not take into account the contrast decreasing effect of the atmosphere. Also, the effect of disability glare (due to the straylight in the observer's eye) and the veiling light produced by the windscreen of the car, are not considered. In this study the influence of these three contrast decreasing factors are discussed and, for some typical examples, the contrast reduction is calculated. (A)