Visibility at a tunnel entrance: Effect of temporal adaptation

Abstract

We describe a dynamic study of the effect of temporal adaptation on the detection threshold for an object (disk or gratings) in continuously variable luminous surroundings. Two types of visibility threshold were determined: dynamic thresholds, in a nonadapting situation (temporal effect); static thresholds, in conditions of steady adaptation. Two different profiles simulating variations in the luminous surroundings were tested. A transitory increase in the curve of relative threshold versus time was observed. The overshoot amplitude and the position of its maximum in time vary with the test and the luminous profiles selected. The effect of temporal adaptation, evaluated from the overshoot parameters, could play a significant role in practice and lead lighting engineers to enhance luminous levels in the first few hundred meters inside the tunnel entrance.