Calibration of Luminance Meters for Lighting Control in Road Tunnels

The report describes the construction of a stand for calibrating L20 and Lth luminance meters used in daylight tunnel lighting control systems. The adaptation luminance L20 of a motor vehicle driver before entering a road tunnel is an important parameter for safe passage through the tunnel tube, measured with an uncertainty of up to 3%. Measuring higher than the actual values leads to over-consumption of energy due to the operation of the daylighting with a higher power. The measurement of lower L20 values than the actual ones cause the daytime running lights to work at a lower power and is therefore a prerequisite for unfortunate accidents due to impaired visual adaptation of the motor vehicle driver. The luminance of the roadway in the entrance area of the tunnel Lth is measured periodically to check the state of daylight and compliance with the required ratio k=Lth/L20 by the lighting control system - k is a key indicator for safe adaptation to the illuminance levels in the tunnel when changing the adaptation luminance L20, a function of the natural illuminance in front of the tunnel entrance (Enat. =2-100 klx).