Based on the perceived contrast method in road tunnel lighting, Commission Internationale de l^¢Eclairage (CIE) defined the contrast revealing coefficient q_c. The research report CIE 189-2010 recommended that contrast revealing coefficient q_c was one of the indicators of tunnel lighting quality evaluation system. Many studies suggested that the value of q_c was 0.6 under counter-beam lighting in tunnel lighting threshold zone. The value of contrast revealing coefficient was 0.2 under symmetric lighting. However, no studies have recommended the optimal value of contrast revealing coefficient under different lighting systems. The optimal value of contrast revealing coefficient was closely related to visual efficacy and driving safety in road tunnel lighting. Based on the range values of contrast revealing coefficient and visual efficacy experiment, this paper aimed to study the optimal values of contrast revealing coefficient under different lighting systems. The research results were as follows: the optimal value of contrast revealing coefficient qc was 0.20 under symmetric lighting and theoptimal value of q_c was 0.85 under counter-beam lighting. The optimal value of contrast revealing coefficient was 0.17 under pro-beam lighting.