Abstract
In Japan, since 1958 lighting problems on the autoway-tunnels have occurred concerning the constructions of the express-ways, such as the Tokyo express highway or the Meishin expressway. The first experiments were carried out for the purpose of measuring the recovering time of the visual acuity after the sudden change of brightness.For the light adaptation, the adopting field was illuminated with a maximum 30.000 1x using a projector with lk.w. incandescent lamp. The second experiments were carried out for the purpose of finding such brightness reduction as keeps the visual acuity at practical degree.