The design of lighting installations in tunnels for motorised traffic requires critical compromises between safety and lighting costs. During daytime the lighting level in the first part of the tunnel shall be high enough to compensate visual adaptation. The CIE 88 technical report (CIE, 2004), the European technical report CR 14380 (CEN, 2003) and several national standards, like the Italian UNI 11095 (UNI 2019) correlate the lighting level in the threshold zone with the veiling luminance evaluated in the access zone, i.e. in the zone in front of the tunnel portal with a length equal to the stopping distance. The measurement of the veiling luminance is greatly simplified using Image Luminance Measuring Devices (ILMDs) but its evaluation for the design specification of the lighting installation is a task not adequately described in standards. Some possible approaches are described and compared considering different available data and simplifications.
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