# Effects of Sidewall Brightness on LED Lighting Environment and Visual Performance in Road Tunnels
## 2 Test Arrangement
### Experimental Scheme  
After the energy-storage and luminescent coating and gray cloth were decorated on the tunnel sidewalls, the material reflectance was measured to be 0.9 and 0.3 for the coating and cloth, respectively, by the C84-III reflectance tester (see Figure 4a). The test was carried out after 8 p.m. to avoid the influence of natural light on the lighting environment in the tunnel. The tested indexes of the lighting environment mainly include the illuminance and luminance in tunnel, and the spectral distribution and S/P value of LED light sources. The illuminance and luminance in tunnel were measured by the CL-500A illuminance meter and LM-3 luminance meter, respectively (see Figure 4b,c), and three cross-section positions of 55 m, 65 m and 75 m away from the tunnel entrance were selected for the measurement. In each cross-section, the measuring points for the illuminance and luminance of road surface were the center of the pavement and the left and right sides which are 2 m from the center (see Figure 1), and there were nine measuring points for the pavement. The sidewall measuring points were at the height of 1.5 m on the left and right sidewalls (see Figure 1) with a total of six measuring points of the three cross-sections. In the testing of sidewall and pavement illuminance, the optical probe of the illuminance meter was along the vertical direction of the sidewall and pavement, respectively. The spectral distribution and S/P value of the LED light sources were measured by the OHSP-350Z multifunctional spectrometer (see Figure 4d), and the measured position was selected at the cross-section of 65 m away from the tunnel entrance. The test for human visual characteristics includes two parts: the visible distance test for a small object in the tunnel and the dynamic change of the driver's eye pupil diameter during driving in the tunnel. When testing the visible distance for the small object, three observers with normal sight and without color blindness, color weakness, or other eye diseases stood outside the tunnel with a distance of 38 m away from the tunnel entrance and observed the small object randomly placed in the tunnel, as shown in Figure 5. The  
Figure 4: Testing devices for lighting environment parameters in tunnel. (**a**) Reflectance tester, (**b**) illuminance meter, (**c**) luminance meter, (**d**) multifunctional spectrometer. Figure 3: Light distribution curve of LED lamps. small object is a gray cube with a size of 10 cm \(\times\) 10 cm \(\times\) 10 cm and a surface reflectivity of 0.2 [19]. The observer firstly stood outside the tunnel and a black cloth was placed in front of him; then, the black cloth was removed, and the observer was requested to recognize the small object randomly placed on the pavement of the tunnel for 0.1 s [19; 30]. The observer was asked the following three questions: (1) Is there any object? (2) Where is the position of the object on the pavement? and (3) What is the shape and color of the object? If the three questions were answered correctly, it was considered that the observer can recognize the small object [19]. During the test, the distance between the small object and the observer was repeatedly adjusted until the observer cannot recognize the small object, and then recorded the maximum visible distance between the observer and the small object. When testing the dynamic change of driver's eye pupil diameter during driving, one of the three observers who had the longest driving age and was the most skilled at driving was selected as the test object. The Tobii Pro Glasses 3 eye tracker (see Figure 6a), which can realize high-quality eye tracking and ensure accurate and stable eye tracking data, was used. Before the test, the driver parked the vehicle at the entrance of the tunnel, then wore the eye tracker and calibrated it, as shown in Figure 6b. Subsequently, the driver started the vehicle and drove at a constant speed in the tunnel. Driving to the position about 40 m from the tunnel exit, the driver began to brake until the vehicle stopped.