The Evaluation of the Lighting at the Entrance of Very Long Tunnels

Background: One of the major topics related to the very long tunnels is dark hole effect. This is a common phenomenon caused by the sunlight reflected from the surroundings of the tunnel to the eyes of drivers and the lack of sufficient light at the tunnels' entrance, which decreases the contrast of barriers inside the tunnel and also makes it difficult to see potential obstacles at the entrance. The result is an increased risk of traffic accidents in these tunnels. Therefore, the aim of this research is to subjectively assessment the safe rate of lighting in one of the very long tunnels located in the province of Ilam. Methods: To subject evaluation the safe rate of lighting at the tunnel entrances, two parameters of the average luminance of tunnel entrance and equivalent luminance are required. In this study, Luminancemeter device model S3 was used to measure the average luminance of tunnel entrance. Then, to calculate the equivalent luminance, a YASHICA108 camera with a 35 mm lens was photographed at a distance between the tunnel entrance and a safe stopping point, and then the Holliday polar diagram was used to calculate equivalent luminance (accordance with the standard CIE88-2004). Results: In this study, the average luminance at tunnel's entrance was equal to 17 , the luminance was equal to 127.5  Using the ADRENAL equation, the quality of lightening at the tunnel entrance was less than 1. Conclusion: Comparison of the results obtained from the healthy and safety rate of lighting levels at the tunnel's entrance with the De Boer mental scale indicated that a dark hole effect occurs at the entrance of the tunnel under investigation and the light sources installed at the entrance of this tunnel did not have the sufficient ability to inhibit the dark hole effect.