In order to study the effects of tunnel illumination for visibility under low transmission, and to provide the theoretical basis for tunnel illumination brightness adjustment under low permeability conditions, two cameras with different spectral characteristics were used to be detectors for obtaining the relationship of observation transmittance, lighting levels, the target/background contrast. The results show that the target/background contrast increases with the increase of lighting luminance, there is nonlinear relationship between the two; the maximum value of the target/background contrast that can be achieved is limited by transmission; Improving the target/background contrast and the visibility by increasing lighting luminance can only be effective in a certain brightness range. According to the experiments it is concluded that improving lighting brightness has little effect on visibility under the condition of high lighting level, under the condition of low lighting level, improving the lighting luminance can effectively improve visibility. The lighting luminance should be adjusted in proportion on the base of the concentration of smoke and transmission in order to ensure visibility and driving safety.