# Influence of Headlight Level on Object Detection in Urban Traffic at Night
## 1 Introduction  
The visual system is an essential source of information for vehicle drivers in road traffic [1, 2]. In order to ensure adequate visibility conditions for vehicle drivers under different lighting conditions (day and night), various lighting systems are used. On the one hand, street lighting systems are used in urban areas, which provide a lighting situation at night for all road users involved (motorists, pedestrians, cyclists). On the other hand, motor vehicle headlights are used to provide drivers with a suitable lighting situation, enabling the detection of obstacles and early reaction during driving [3]. The detection of obstacles requires a certain threshold luminance difference between the object and its environment, which depends on various factors. For example, adaptation luminance, object size, presentation time, observer age, and contrast polarity play a crucial role in object detection [1, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13]. Several studies and analyses of traffic accident statistics show that increased adaptation luminance reduces the required contrast by increasing brightness, thereby reducing the risk of nighttime traffic accidents [14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25]. For example, analyses by [PERSON] [26] show that in the range of roadway luminance from 0.5 to 2.0 cd m\({}^{-2}\) there is a direct correlation between roadway luminance and the night/day crash ratio; moreover, an increase in roadway luminance of 1.0 cd m\({}^{-2}\) results in a reduction in this ratio of approximately 35 %. Similar results regarding the reduction of the required contrast at higher roadway or adaptation luminances can be found in studies by [PERSON] [13] or [PERSON] [27]. Studies on the influence of object size by [PERSON] [11], [PERSON] [27], and [PERSON] et al. [28], as well as [PERSON] [29] on the required threshold luminancedifference, show that larger objects reduce the threshold luminance difference. However, it is important to distinguish between [PERSON]'s range, where object size has an effect, and [PERSON]'s range, where the effect of object size is negligible [30; 31]. Studies by [PERSON] [12], [PERSON] and [PERSON] [32], [PERSON] [33], and [PERSON] [34] have demonstrated the influence of age on the detection of objects in nighttime traffic. [PERSON] and [PERSON] conducted a study with 235 observers of different ages. Analyzing the results for 234 of the 235 observers, they found that the visibility multiplier increases with age. Their study was performed with 4-minute Landolt rings at a background luminance of 100 cd m\({}^{-2}\). Observers were asked to indicate recognition by a forced-choice procedure. It is noteworthy that the slope of the multiplier increased significantly from the age of 64 [32]. Contrast polarity affects the threshold luminance difference required for object detection as well [11; 13; 35]. Studies by [PERSON] [11] and [PERSON] [13] show that the threshold luminance difference for positive and negative contrast is of the same order of magnitude, and is smaller for negative contrast than for positive contrast. These influence parameters have been incorporated into detection models by various researchers and research groups in order to make statements about the detectability of objects [30; 36; 37; 38]. One of the most commonly used models is [PERSON]'s Small Target Visibility Model [30].