# Influence of Headlight Level on Object Detection in Urban Traffic at Night
## 3 Results
### Subject Study Results  
In the next step, the subject responses are used to consider the actual detection probabilities for the flat targets. For this purpose, the proportions of the detected flat targets in the sixteen different positions are calculated for the two cases, namely, low beam switched off and low beam fully switched on. In order to determine the proportion of detected positions, the first step is to calculate the number out of the fourteen test subjects who detect the object at each position with the low beam switched off versus with it fully switched on. This results in a certain detection probability for each object position. For example, a detection probability of 85.7 % results if 12 out of 14 test subjects detect the object. The number of object positions with a detection probability greater than the threshold considered can then be summed up. Threshold detection probabilities \(p\) of 90 %, 75 %, and 50 % are used for this purpose. The threshold of 90 % represents the threshold for secure detection, 75 % the threshold for acceptable detection, and 50 % the critical threshold which must not be undercut, as this means that the object is not detected in a majority of cases. The results of this consideration are shown in Table 8 for vehicle position 1 and in Table 9 for vehicle position 2. Table 8 shows directly that with the low beam switched off in vehicle position 1, the negative contrast generated by the road lighting leads to more detected objects on all sixteen positions than the fully switched on low beam for all three test roads and all probabilities considered. This is especially evident for test road 1, with an average roadway luminance of 0.91 cd m\({}^{-2}\). Here, with the low beam fully switched on, only the flat targets on 6 out of 16 object positions are detected with a probability of over 90%, while with the low beam switched off the flat targets are already detected on 15 out of 16 object positions with a probability of over 90%. It is noticeable that with the low beam switched on, the detection probability for the flat targets is above the critical threshold of 50% on only 12 out of 16 positions on test road 1. Looking at the darker test roads, it can be seen that the number of objects detected with the considered probabilities are in a similar range for both switched off and fully switched on low beam. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{3}{c}{Low Beam off} \\ \hline  & 20 m & 35 m & 45 m & 55 m \\ \hline \(-\)3.0 m & 35.55 & 25.72 & 14.26 & 13.59 \\ \(-\)1.5 m & 40.44 & 28.85 & 14.88 & 13.81 \\
0.0 m & 48.72 & 33.94 & 13.56 & 17.05 \\
1.5 m & 51.41 & 35.78 & 18.84 & 18.91 \\ \hline \multicolumn{5}{c}{Low Beam fully switched on} \\ \hline  & 20 m & 35 m & 45 m & 55 m \\ \hline \(-\)3.0 m & 56.08 & 33.68 & 15.98 & 8.89 \\ \(-\)1.5 m & 169.47 & 38.68 & 19.74 & 8.77 \\
0.0 m & 151.08 & 28.92 & 21.36 & 4.95 \\
1.5 m & 95.21 & 23.50 & 19.70 & 2.58 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Calculated Visibility Levels for test road 3, vehicle position 2. Table 9 shows that the results for vehicle position 2 with the low beam switched off are very similar to those for vehicle position 1. On both test roads 1 and 2, one additional object position is detected with a probability of over 90 %, meaning that the flat targets are now securely detected on all sixteen object positions for vehicle position 2 on test road 1, while on test road 2 this is the case for 13 out of 16 object positions. It is noticeable that in vehicle position 2 with fully switched on low beam the flat targets can be detected on more object positions than in vehicle position 1 on all three test roads. The reason for this observation can be found in the reduced distance to the object positions, as the objects are illuminated with a higher intensity when the low beam is fully switched on than when the vehicle is in position 1 due to the photometric distance law.