## 4 Discussion  
The current research aimed to establish a link between subjective glare perception in nighttime road traffic following glare by different light sources and objective psychophysiological indicators of stress known from the literature, such as SCR or blinking rate [5, 6, 7, 8, 9], in a sample of Czech drivers. Therefore, a laboratory within-subject experimental design was used, employing physiological data collection and visual acuity and contrast sensitivity charts, as well as the de Boer scale for subjective rating of perceived discomfort glare [18, 19, 23]. We specifically aimed to test whether the complaints of drivers on the internet [10] about being glared by \"modern car headlamps\" would be replicable in a controlled laboratory setting. Among other factors, we have hypothesized that being used to either halogen bulb reflectors or LEDs as \"own car lights\" might influence the perception of glare by the oncoming vehicle. Based on our results, such a pre-adaptation effect does not take place. Subjectively, the light sources perceived as the least glaring were the halogen bulb reflectors (also having the lowest CCT of the sources used), which is consistent with previous research [10, 14, 16]. No difference in subjective glare rating was observed among the three LED modules (\"white\", \"yellowish\", and \"bluish\"). However, it is noteworthy to say that due to the way the LED modules were powered, sources of different CCTs used within the experiment did not have the same luminosity at the photometric point B50L. In fact, the luminosity of the LED source with the lowest CCT (\"yellowish\") was twice the luminosity of the highest CCT LED source (\"bluish\"). In that context, it seems advantageous to use more yellow LED bins in car headlamps, as the subjective perception of the drivers' glare might be comparable to other LED bins, but the effectivity in terms of luminosity might be higher. As for psychophysiological reactions to glare, blinking frequency--seemingly one of the common-sense reactions to glare--did not differ between the light samples used. It did, however, correlate weakly with the SCR, indicating that blinking decreases with a higher stress response. This would be consistent with [9], although, in their research, blinking frequency was significantly lower in the condition of higher visual discomfort. We did not find such an association between blinking frequency and subjective discomfort glare rating. For further research, however, we recommend also employing some sort of a cognitive load task in the experimental procedure, as this was found to further influence blinking frequency [9] and also seems to better reflect the driving task itself, as we argue further below. Skin conductivity response changes depended significantly only on the light of the oncoming vehicle, where the serial \"white\" LED module seemed to produce lower SCR than other light sources or light source combinations. Further, the SCR did not correlate with the subjective de Boer glare ratings. This might seem surprising, as we have expected a more pronounced stress reaction following glare [5, 8, 9, 21] and at least some degree of correlation between the subjective glare perception and the objectively measurable reaction. We originally intended to include sympathetic and parasympathetic activity measures derived from heart rate variability (specifically the LF/HF ratio), but our data turned out to be incompatible with this analysis. HRV is usually extracted from periods notably longer than 30 s (as used in our design), because the slowest LF wave (0.04 Hz) appears in the recording once per 25 s [6]. Therefore, our recording's length is not sufficient to reliably derive the LF spectral density. In the case of such a short time period, other cardiac measurements of stress might be more suitable, such as the evoked cardiac responses [40].