Study On The Computing Method Of Luminance Of Tunnel Threshold Zone

Highway tunnel has many advantages, as shorten mileage, save time, improve transport efficiency, save space and effectively protect the ecological environment, etc. The primary purpose of highway tunnel lighting is provided a good visibility for various vehicles, reach the purpose of safety, comfort and quick operation, and beautify the environment. The tunnel lighting in threshold zone is beau for study. This paper introduced the characteristic of tunnel lighting, country and outside development process of the tunnel lighting in threshold zone, as well as the urgent situation of tunnel lighting energy-saving. Foreign highway tunnel lighting technology as early as the start of the study, after many years study and practice, technology is mature, but our country research start to late relatively, lack of experience and basic work, national standards are norm.This paper describes the three calculating method of the tunnel threshold zone luminance which were recommended by International Commission on Illumination - the method of k value, SRN subjective evaluation and contrast detection, and the formula for the three methods, and the calculation parameters. Comparison of different countries have adopted the k value, found that China's existing norms choose the k value no scientific basis; SRN subjective evaluation is decided by visual experience, its accuracy still needs to be deliberated, but contrast detection consider a variety of environmental factors, which is most suitable to calculate the tunnel threshold zone.This paper analyses the various factors which impact of driver's eyes when driver close to the tunnel in the natural lighting environment, and in the process of use the contrast detection method calculate the tunnel threshold zone luminance, these factors transit into the calculation parameters. This paper introduced a method of measurement of atmospheric luminance and atmospheric transmission rate by digital camera, as well as the atmospheric transmission rate formula. The transmission rate of car windshields, two commonly used roads, as well as the reflection coefficient of the three-form lamps with the L / EV coefficients were measured and compared with the literature, Finding that the latter two parameters are consistent with the literature data range, and car windshields as the impact of sunscreen films have certain differences.In this paper, using computer simulation technology for the smallest contrast detection experiments of the human eye to determine the important parameters Cm in the model of tunnel threshold zone luminance at the positive and negative contrast environment. Using the computer program to simulate Schreuder's tunnel simulation experiment, through regression analysis of the measured data obtained the smallest perceived contrast data in the positive and negative contrast conditions and identifying different probabilities, the tunnel threshold zone's background luminance - L1 is 4000 cd/m2, the visual angle of computer screen (used to simulate tunnel entrance) is 1°×45', the visual angle of target is 7'×7'.Use the ratio of perceived contrast CP is a constant in the same background luminance and the different perceived probability, select a baseline perceived probability, determine the relationship between baseline perceived probability and other perceived probability, through comparison the perceived contrast of other perceived probability of baseline perceived probability. Ultimately, through regression analysis of the experimental data obtained P = 75% of the perceived contrast data. And determine the smallest perceived contrast Cm is 25.36% at the positive condition, and the smallest perceived contrast is 22.70% at the negative condition for perceived probability was 75%.In order to test the practicality and scientific of contrast detection method of tunnel threshold zone luminance, applied research to Zhenwushan Tunnel as an example, the real-tunnel environment was measured and calculated. The tunnel threshold zone luminance is calculated using three methods, found that the method of k value by CIE recommended have the maximum luminance, The tunnel threshold zone luminance with SRN subjective evaluation method has greater difference, the detection contrast method is most suitable, because it consider a variety of factors.