189 street & urban lighting Tunnel lighting system threshold zone 20° external transition zone interior zone exit zone Driled small Driled big The purpose of the lighting at the initial section of the tunnel is to prevent the ‘black hole’ effect, in other words, the abrupt change from the outdoor daytime lighting conditions to the darkness of the tunnel. This is called reinforcement lighting. This area of the tunnel is undoubtedly the most critical if not correctly lit and it represents one of the predominant causes in most accidents which occur in it. The function of the permanent lighting is to light the street for the driver’s eye after it has already adjusted to the change of brightness after entering the tunnel. This is present along the entire length of the tunnel and, during the day, in the initial section that corresponds to the entrance and transition zones, it is integrated by the reinforcement lighting to ensure correct perception of the obstacles. The driver arriving at the internal zone has by now become accustomed to the lighting levels similar to night driving and is therefore in a situation where constant, uniform and comfortable lighting is required that does not change until the exit zone. To ensure reinforcement lighting, proflow or counterflow optics systems are used. Proflow lighting is achieved with a distribution in which glare is reduced to a minimum in that the light beam is aimed in the driving direction. Counterflow, on the other hand, is achieved with distribution in which the maximum peak of brightness intensity is aimed in the opposite direction. In this latter case, the obstacles placed inside the tunnel are highlighted as dark objects on the lit road surface and are therefore highly visible, reaching high negative contrast values. The main principle of tunnel lighting is to ensure that the driver has the same visual perception inside and outside the tunnel. The difference in brightness between these two zones (during the day) is often too great for the human eye to be able to distinguish any obstacles inside the tunnel and the time when entering the tunnel is too brief to allow the eye to adapt to the different lighting levels. The DriLed article can be used to light the different zones of tunnels. What makes them stand out in light emission and perception is how they are applied in the tunnel, where the required lighting differs from zone to zone.
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