Research Of Atmospheric Transmittance Based On Perceived Contrast Method Of Tunnel Lighting

This paper is supported by the National Natural Science Foundation of China, ″Research on Perceived Contrast Method of Tunnel Lighting″.The tunnel threshold zone is the starting point for the entire tunnel, the luminance in threshold zone is the foundation of tunnel lighting design.For the three caculating methods of the tunnel threshold zone luminance —— the method of k value,SRN subjective evaluation and the perceived contrast method which were recommended by CIE, the perceived contrast method,which could truthfully reflect the driver′s visual environment near the tunnel portal and comprehensively take into consideration of various factors affecting the driver′s perceived ability,is the most suitable method to ensure the tunnel threshold zone luminance at present.The near-surface atmospheric transmittance of one stopping sight distance, τatm(0.1) as an important parameter in the perceived contrast formula,has a major impact on the calculation result of tunnel threshold zone luminance.As to the parameter′s value, the recommended value once given by CIE88-2004 publication is 1.0.However, the atmospheric transmittance τatm is belong to the atmospheric optical parameter,and its value has a change as atmospheric conditions,weather conditions, or geographic environment changes.Therefore,the author think,the recommended value of 1.0 has some reference significance,but the accuracy and universality of 1.0 are questionable.In order to determine the reasonable values of τatm(0.1) under different weather conditions,the paper which focuses on τatm,firstly obtains several caculation methods through analysising and summarizing related theories,and eventually confirms that the calculation method of atmospheric visual theory with strong operability is the most suitable method for this study.Then,according to the core formula of atmospheric visual theory,the basic calculation model of τatm is deduced,which plays an important role on later data process.Based on the existing research findings,various factors of τatm,such as relative humidity,temperature,and wind speed,are summed up.In terms of practical measurement,the experimental research of τatm,taking Chongqing region as an example,is conducted in six typical weather conditions.By analyzing the experimental data,the paper sets up the function relation between the atmospheric transmittance τatm and the atmospheric visibility V,which could be a new method to calculate τatm(0.1). According to the calculation method,the author works out the value ranges of τatm(0.1) under different weather conditions.At last,from the perspective of energy saving and safety,the author analysises and discusses the influence of τatm(0.1) under different weather conditions on the tunnel threshold zone luminance.Besides,the author applies the calculated value of τatm(0.1) on Zhenwu Mountain Tunnel. In addition,based on the study results,the author puts forward several suggestions and requirements on the tunnel lighting design.