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LIGHTING AND SURFACE DESIGN OF TUNNELS
TUNNEL LIGHTING – RESEARCH STUDY
this direction of radiation considerably less luminous flux and thus electrical power is required for the same roadway luminance. The basis for this principle is based on the slightly specular road surface (for example R3). As a result, roadway areas that are specularly illuminated towards the observer ”shine”. The flatter they are illuminated, the higher the luminance of the roadway due to this ”specularity effect”. In the USA, studies in the 1960s led to the concept of ”Small Target Visibility” (STV) [10]. Subsequently the ”Visibility Level” (VL) derived from this was introduced as the main criterion for the quality of street lighting [11]. Small vertical panels were set up on the road surface as visual objects and illuminated against the direction of travel, and the visibility was evaluated as a function of the illumination in a stationary manner. The observer sees the visual object (panel) from its shadow side (negative contrast), while the road appears bright. Visibility now depends on the difference in luminance between the object (panel) and its background (road surface) and is better the greater the background luminance (road surface luminance) [12]. These considerations were based on obstacles on an empty roadway; today’s situation in densely trafficked tunnels is completely different; here it is more a matter of spatial perception, optical guidance, and visibility of the vehicles ahead. The counter-beam principle [13,14] aims solely at achieving a target value for the roadway luminance (standard) as efficiently as possible but disregards an overall perception of the tunnel space. Uneven luminance on the carriageway and in the field of vision, glare, and poor object recognition (the rear of vehicles ahead is dark, see Figure 12) are the result of this lighting principle, and a ”stable” spatial perception cannot be achieved with it. In the pro-beam principle [6,13], the high vertical illuminance levels provide very good spatial perception and object recognition. The optimized pro-beam luminaire is perfectly glare-free and is not perceived directly by the driver, there is no longer any increased luminance in the field of vision, and optimal adaptation (stable perception) occurs (Figure 13 and Figure 14). In the dynamic tunnel model at Bartenbach in Aldrans, you can see these effects for yourself (Figure 15). Instead of the vehicles, the lighting moves in this model. When looking in, the deceptively real impression is created that the vehicles and
Issue 88/Nov-Dec/2021
Figure 11: Relative reaction times for correct responses in the visual performance test (numbering according to Figure 8). The differences are highly significant, the third and fourth variants are equivalent (red crossbars).
Figure 12: Concept counter-beam principle.
Figure 13: Concept of the pro-beam principle.
Figure 14: Counter-beam (left) and pro-beam (right) lighting in the dynamic tunnel model Bartenbach.
the observer are moving through the tunnel. By appropriately controlling individual optics with different light distributions that are arranged very closely together, different speeds of passage can be simulated with different intensities, beam distributions and luminaire spacing. A significant improvement of the actual situation would be a so-called ”adaptive tunnel lighting” as a compromise between the ”high-end solution in terms of perception psychology” (pro-beam principle) and an economically reasonable solution under the current standardisation situation: in the entrance areas, where a high adaptive luminance (transition from the bright outdoor area to the dark indoor area) is most im-
Figure 15: Dynamic tunnel model at Bartenbach.
portant, the counter-beam principle could be applied; in the indoor area, depending on the traffic density, a mixture of co-beam (high traffic volume) and counter-beam (low traffic volume) lighting could be used.
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