## 2 Materials and Methods
### Laboratory Setting  
In order to conduct research on glare and its underlying psychophysiological mechanisms, we used a laboratory setting with two separate rooms. In the smaller room, an initial screening of the participant's driving experience and vision characteristics was performed (see Section 2.3 below). After this initial examination, the participants were taken to the larger laboratory room simulating a two-lane night-traffic road scenario for the glare experiment itself. This room was 5 \(\times\) 10 m, light-tight, and painted with matte black color. At each end of the room, a carousel with mounted light samples was placed to simulate the headlamps of the \"driver\" (in the right lane) and those of the \"oncoming vehicle\" in the left lane; see Figure 2. Although the carousel of the \"oncoming vehicle\" could, in principle, be moving forward, it was decided to keep it in place, approx. 10 m away from the driver's position, for the whole experiment to simplify the procedure. The participant (\"driver\") was seated behind a stand with their head placed on a chin rest (110 cm above the ground and 150 cm behind the driver's carousel) in order to fix the position of the head during the experiment. On both sides of the stand, approximately at the driver's eye level, light meter sensors were placed to continually measure the amount of light coming to the driver's eyes (sampling frequency of 50 ms) and to help pinpoint the exact moment of glare. Based on a pilot study with three drivers, the threshold for glare was set at 10 lux (counted as the average value from both sensors). Figure 1: Participant distribution by age and gender. The light samples used in the experiment were prepared to be as close to the real headlamps used in the vehicles seen on the roads as possible (compact and subcompact cars). To be able to compare driver's glare perception, a typical halogen reflector with an H7 bulb was used along with the newest LED projector modules. The LED projector modules were conventional in the sense that they did not contain any matrix capabilities to dim the beam while oncoming traffic is approaching. In the experiment, only low beams were tested. The aim was to determine whether there is a significant difference between observing a reflector and projector headlamp of the same car and whether any change towards the blue or yellow part of the LED color spectrum (i.e., closer to the color of a halogen bulb reflector headlamp) will cause the headlamps to impose more or less glare compared to the variant used in the series production (\"white\" LEDs). To assess the impact of the light distribution's color, the series LED projection modules needed to be adjusted. In order to be able to use the same electronics for each projector module (printed circuit boards--PCBs with the original driving circuits), automotive-grade LEDs from the same manufacturer were chosen rather than prototype full-spectrum LEDs. The limitation of this approach was that each of the tested LEDs had a peak in the blue part of the spectrum. Nevertheless, LEDs from the most yellowish and the most bluish color bins (that are not used in the series production) were chosen to be compared with the series white LEDs, and their correlated color temperatures (CCT) were approximated using [PERSON]'s formula [24]. Moreover, the projection optics in the experimental modules were refocused. Modules with the bluish color bin LEDs were focused so that the gradient of the light distribution was increased (the distribution was sharpened). Conversely, modules with the most yellowish color bin were defocused (the distribution was blurred). This allowed for the assessment of how extreme adjustments of the series LED projection modules can make glare perception nearer or further from the halogen reflector glare experience. All of the samples were prepared with the goal of meeting the standard photometric limits described in the ECE norms (see Table 1).