# Influence of Headlight Level on Object Detection in Urban Traffic at Night
## 4 Discussion  
This section revisits and answers the research questions raised at the outset. 1. What is the influence of different road illumination levels and luminous intensities of motor vehicle headlights on the detection of objects at different distances and angular positions in front of the vehicle? From the results of this study, it is evident that the effectiveness of the low beam is strongly dependent on the illumination level of the road, which is generated by the existing street lighting. Thus, it can be seen that on brightly illuminated roads, such as test road 1, the effectiveness of the fully switched on low beam is rather low compared to the switched off low beam, as here the existing street lighting already generates a strong negative contrast and enables the detection of the objects. This can be seen in Tables 8 and 9; in vehicle position 1 and with low beam switched off, objects can be securely detected in 15 out of 16 positions (detection probability \(>\) 90 %), while this is only possible in 6 out of 16 positions when the low beam is fully switched on. If the distance to the measuring grid is shortened (vehicle position 2), the effectiveness of the low beam increases to such an extent that objects can now be securely detected in 12 out of 16 positions. The reason for this is that at shorter distances the low beam is able to produce higher vertical illuminances on the objects, enhancing the positive contrast. Thus, the results of [PERSON] et al. [56], [PERSON] et al. [57], and [PERSON] et al. [62; 63; 64] can be confirmed, that is, the low beam of vehicle headlights have higher efficiency at shorter distances. In addition to the shorter distance, a lower illumination level of the road increases the effectiveness of the low beam. The proportion of securely detectable objects increases from 6 (test road 1, 0.91 cd m\({}^{-2}\)) to 10 (test road 2, 0.53 cd m\({}^{-2}\)) to 12 out of 16 positions (test road 3, 0.38 cd m\({}^{-2}\)) for vehicle position 1. The same trend results for vehicle position 2. Here, the number increases from 12 (test road 1) to 13 (test road 2) to 15 (test road 3) out of 16 positions with secure object detection. This correlation between the illumination level of the road and low beam  
Figure 10: Object position 15 on test road 2; detection conditions are made more difficult by the position of the flat target directly in front of the fixation object. effectiveness has previously been shown by [PERSON] [53]. Thus, the present study confirms previous findings in the literature showing that low beam effectiveness decreases as the level of illumination increases. If the detection conditions are considered as a function of distance and object angle, no direct dependency can be determined due to the high variability and complexity of the lighting scenarios in urban traffic areas. Here, only tendencies based on the Visibility Level observation can be identified. The results for the switched off low beam on all test roads show that the object positions, which are located on the right side of the road, have higher Visibility Levels; this is because on all three test roads the street lighting systems are located on the right side. The higher Visibility Level values tend to shift to the center of the road when the low beam is fully switched on due to the light distribution of the headlights. Thus, the findings of [PERSON] [51, 52], [PERSON] [53], [PERSON] [35, 55], [PERSON] et al. [56], [PERSON] et al. [57], and [PERSON] [13] can be confirmed based on the results of the present study. While street lighting alone provides sufficient detection conditions in urban traffic areas, the combination of street lighting and automotive lighting is in many cases associated with a deterioration in detection conditions due to the resulting contrast reduction. What influence does the intensity of the low beam have on the contrast polarity and value of flat detection targets on illuminated roads with different illumination levels?