A measurement method for recording adaptation luminances at road tunnels under actual traffic conditions is described and the application of the results discussed. For conducting the survey, a photometer with a recording instrument was installed in a vehicle. The luminance of the road track, the tunnel walls can be recorded, and also, with a glare lens, the veiling luminance. The measurements were made from the driver's position taking into account effects caused by the vehicle (windscreen, etc.) and the speed. Recordings of a tunnel can be conducted in a relatively short time, so that the flow of traffic is not impaired. With the assessed luminance data the adaptation luminance can be calculated and different tunnels can be compared. To characterise a tunnel under physio-optical aspects, a criterion is proposed.