A typical method to measure human visual ability discriminating brightness is to enable examinees to watch one uniform illumination plane adequately covering the whole vision. This plane itself looks like a nubuck glass having a good diffuse reflectance and is illuminated from behind by one lighting source whose intensity is changeable and denoted by I. When adding an incremental intensity I to the uniform illumination plane, examinees will observe a bright spot in the center of the plane as shown in Fig. 1. If the I is very small, examinees will say “cannot observe a bright spot”. However, with the I increasing, examinees will be gradually sure that they can observe it. If the I is strong enough, all examinees will positively answer that they do find it. I50 is defined as incremental brightness intensity, namely the vision threshold, meaning that more than 50% of examinees answer that they can observe the bright spot in a given illumination background (Zhang, 1999). As a result, reliable evidences of visual reflection can be gained by asking examinees to identify the target area from a given background. Based on this principle, test cards for vision threshold were designed to determine the brightness recognition capacity of examinee’s vision