## 1 Introduction  
The visual system is the main source of information when driving a motor vehicle. It is used to detect potential risks at an early stage and to initiate an adjustment of the driving behavior [1; 2; 3; 4; 5; 6; 7]. Adequate visibility conditions are necessary for the visual system to perform its task reliably. To ensure these visibility conditions, especially in road traffic at night, motor vehicle headmaps are used. In this context, traffic in non-urban areas is of particular relevance, since vehicle headlamps are the only source of illumination that creates the detection conditions for the driver. Object detection describes the visual perception of luminance differences in the visual field. The smallest perceptible luminance difference between a visual sign (\"object\") and its environment is called the detection threshold. Thereby, the quantitative description of the detection conditions is made by different contrast definitions. The definition of the Weber contrast \(C_{W}\), which describes the ratio of the luminance difference \(\Delta L\) between object luminance \(L_{\mathrm{O}}\) and background luminance \(L_{\mathrm{B}}\) to background luminance \(L_{\mathrm{B}}\) (see Equation (1)), is of major relevance for nighttime road traffic [8]. \[C_{W}=\frac{L_{\mathrm{O}}-L_{\mathrm{B}}}{L_{\mathrm{B}}} \tag{1}\]  
Due to the large luminance range that can be used for both the object and the background, two contrast polarities can be realized, which are shown in Figure 1. Thus, positive contrast describes a situation where the object appears brighter than its environment (\(L_{\mathrm{O}}>L_{\mathrm{B}}\)). If the object appears darker than its background (\(L_{\mathrm{O}}<L_{\mathrm{B}}\)), it is called a negative contrast [8]. Object detection depends on various parameters. In addition to the contrast polarity, the adaptation luminance, the object size, the observation time and the age of the observer influence the object detection [1; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19]. Various research and analyses of traffic accident statistics demonstrate that the increased adaptation luminance provides a reduction in the required contrast through higher brightness levels, thus reducing the risk of nighttime traffic accidents [20; 21; 22; 23; 24; 25; 26; 27; 28]. For example, analyses by [PERSON] [29] show that in the roadway luminance range of 0.5 to 2.0 cd m\({}^{-2}\), there is a direct correlation between roadway luminance and the night/day accident ratio, and an increase in the roadway luminance of 1.0 cd m\({}^{-2}\) provides a reduction in this ratio of about 35%. Moreover, studies by [PERSON] [18] or [PERSON] [19] demonstrate similar results regarding the reduction of the required contrast at higher roadway or adaptation luminances. Investigations on the influence of the object size of [PERSON] [15], [PERSON] [19] or [PERSON] [30] on the required threshold luminance difference demonstrate that larger objects lead to a reduction of the threshold luminance difference. However, a distinction must be made between the [PERSON]'s range, where object size has an influence, and the [PERSON]'s range, where the influence of object size is negligible [31; 32]. The age influence on the detection of objects in road traffic at night could be shown by studies of [PERSON] [17], [PERSON] and [PERSON] [33], [PERSON] [34] and [PERSON] [35]. [PERSON] and [PERSON] [33] performed a study with 235 observers of varying ages in this regard. Their analysis of the results for 234 of the 235 observers showed that the multiplier for the visibility threshold increases with age. The study was performed with 4 min Landolt rings on a background luminance of 100 cd m\({}^{-2}\). The observers had the task to indicate the recognition with a forced choice method. It is remarkable that the slope of the multiplier increases significantly from an age of 64 years (see Figure 2) [33]. Contrast polarity also affects the threshold luminance difference required for object detection [15; 18; 36].