The visibility of small objects in a tunnel is a criterion for the design of tunnel lighting. In a former study (See C 19111 (ITRD E206466), 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. 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 contributes to the visibility when the colour factor is larger than 1. This colour factor was calculated for various lighting conditions. Among other things, the results are: 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 (HDN) 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; 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; and for high sky luminances the influence of daylight reaches until 60 m from the entrance, for low sky luminances about 30 m. 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.
Abstract