# Influence of Headlight Level on Object Detection in Urban Traffic at Night
## 4 Discussion
The photometric measurements show that on all test roads there is initially a negative contrast due to the street lighting. If the intensity of the low beam is then increased, the negative contrast is initially reduced in absolute terms until a transition point is reached at which there is no longer any contrast between the object and its background. A further increase in the intensity of the low beam ensures an increase in the positive contrast. However, whether this increase reaches the same amount as the negative contrast that is present when the low beam is switched off depends to a large extent on the illumination level of the road and the distance of the object from the observer. Thus, especially when brightly illuminated roads are combined with higher distances to the detection object, there are cases in which the same amount or even the transition point from negative to positive contrast cannot be achieved; see Figure 6. Because the more brightly illuminated roads result in stronger negative contrasts, the low beam has to compensate for a significantly larger contrast range in order to produce a positive contrast. Thus, the present work confirms [PERSON]'s results [53], which showed that the influence of the low beam decreases with increasing illumination level. This leads to the fact that the increase in low beam intensity on many positions and test roads only leads to a reduction of the contrast amount, worsening the detection conditions. Is there an optimized urban light distribution for motor vehicle headlights, and if so, what should it look like? Because no direct distance or angle dependence can be determined from the data, it does not seem reasonable or possible to generate a generally valid light distribution for urban traffic areas. Moreover, the variation of street lighting is very diverse, and it is complex to consider static headlamp light distributions for optimal illumination due to differences in spacing between street lighting systems and their light point height, luminous flux, and light distribution (see [PERSON] and [PERSON] [69]). In addition, for our three test roads the negative contrast with the low beam switched off is at least as good for the detection of objects in nearly all constellations as that provided by the fully switched on low beam. Therefore, the suggestion resulting from the results of this study would be to reduce the low beam intensity, thereby enabling the detection of objects with the negative contrast. In order not to neglect the visibility of one's own vehicle for other road users or the brightness on the roadway, forefield illumination of the vehicle would be reasonable to increase subjectively perceived safety (cf. [PERSON] et al. [70]). Thus, in addition to ensuring sufficient detection conditions, the driver's sense of safety would be taken into account when generating urban headlight distributions. However, the previous authors are critical of the approach of [PERSON] et al. [62, 63, 64] to reduce the intensity of street lighting. On the one hand, dimming the street lighting in the presence of motor vehicle lighting certainly increases the effectiveness of the low beam and improves the detectability of objects with positive contrast. On the other hand, street lighting in urban traffic areas is responsible for all road users. This includes cyclists and pedestrians as well as vehicles. A reduction in street lighting intensity could lead to a reduction in the subjective feeling of safety for these vulnerable road users, as they could receive the impression that they are no longer sufficiently visible to other road users.