Kleurcontrast in tunnels: nadere berekeningen [Colour contrast in tunnels: additional calculations]

Purpose: The visibility of small objects in a tunnel is a criterion for the design of tunnel lighting. In a former study for the Tunnelling Department of the Civil Engineering Division of the Directorate-General for Public Works and Water Management it was shown that the visibility could be improved when coloured tunnel lighting or coloured objects are used. The current study is a continuation of that study. Methods: The current calculation method of the visibility of the objects is based on the classical luminance contrast of the object. The contribution of colour, in terms of colour hue and saturation, can be taken into account by using the so-called equivalent contrast. The ratio between the equivalent contrast and the luminance contrast is the colour factor. The colour contribute to the visibility when the colour factor is larger than 1. This colour factor was calculated for various lighting conditions. Results: Saturated in pro-beam tunnel lighting provide the highest colour factors, 1.43 for small and 5 for large objects. _ For high-pressure sodium tunnel lighting (HPS) the colour factor is larger than 1 for all object colours, including neutral colours, except close to the tunnel entrance with a high sky luminance. The colour factors are about 1.25 for small and 4 for large objects. _ For neutral colours and a high sky luminance the half of these values are reached at 20 and 15 m, respectively. HDN counter-beam tunnel lighting provides the largest colour contributions for neutral colours. For tunnel lighting with a daylight colour (D65) the colour factor is 1 for neutral colours. Saturated colours in symmetrical and counter-beam lighting score lower with D65 than with HDN tunnel lighting For high sky luminances the influence of the daylight reaches until 60 m from the entrance; for low sky luminances about 30 m. The influence of the atmosphere transmission on the colour factor is negligibly small. The colour factor is fairly independent of the meteorological visibility. Therefore the calculated colour factors are valid for a large visibility range. Conclusion: In order to make the most of the advantages of the colour contribution, it is recommended to use a counter-beam tunnel lighting with a colour that differs from the daylight colour.