Well-designed, high-performance tunnel lighting should ensure thatthe visual perceptions of drivers will be maintained during daytime and nighttime driving conditions, avoiding sudden variations in lighting levels when entering and exiting the tunnel. At night, the luminance level in a tunnel should be constant and equivalent to the level on the road leading into the tunnel. However, since there is a high level of external light during the day, it is necessary to increase the levels of luminance at the tunnel entrance to avoid a "black hole effect" and a reduction of visual perception. At the tunnel exit, the luminance levels should also be increased to help drivers avoid glare effects by the ambient light visible outside the exit portal.
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