###### Abstract  
The broad application of LEDs for automotive lighting purposes, together with new discoveries in vision physiology, is creating new challenges in the field of glare perception. The purpose of this study was to link subjective and objective measures of driver-perceived glare following different light sources used in car headlamps. In order to achieve this, a combination of subjective evaluation using an adapted version of the de Boer scale and objective measures based on psychophysiological data was applied. Predominantly, skin conductance response (SCR), heart rate variability (HRV), and eye-blinking frequency (vertical electrooculography, vEOG) were recorded. Though there was some evidence suggesting lower discomfort with glare from light sources with a lower correlated color temperature, the results were generally inconclusive. This illustrates the urgent need to study the linkage between light source properties and subjective and objective glare measures in deeper detail, so that the technical norms governing car headlamps can reflect the needs of human physiology and psychophysiology. automotive; discomfort glare; lighting; LED; halogen; visual perception; psychophysiology; vision; drivers +
Footnote †: journal: Medical  
to be whiter, or even bluish, compared to the bulbs the drivers were used to [10; 12; 13]. Second, the LEDs are usually mounted within a lens projection module as opposed to a reflector, so that the light-emitting surface is much smaller and, due to the dispersion of light on the plastic optics that are used within the headlamp, produces unwanted effects such as blue color fringing when viewed from certain angles (as might be the case on uneven roads) [12; 14; 15]. At the same time, stimulation of the blue-sensitive S-cones of the retina has been found to be related to greater discomfort perception [16]. Taking these facts into account, efforts toward establishing a reliable methodology to assess discomfort glare by car headlamps have been made since the 1960s [17]. A common tool used in this context is the [PERSON] 9-point rating scale [18], which has been subjected to many revisions over the years regarding the verbal descriptors of the perceived glare intensity, as well as the directionality of the scale (in the original version, \"1\" was described as \"unbearable\" and \"9\" as \"unnoticeable\", which was shown to be confusing for many research participants) [19]. However, the inclusion of physiological data in headlamp glare investigations in order to further validate subjective findings has not been as frequent as one would expect [20], given that these data have been widely used in research on driver fatigue [21] and glare in daylight/indoor conditions [8; 22]. This might be due to the fact that many such studies have been done in the field rather than in a laboratory, but with the increased development of portable physiological signal acquisition devices, one could expect a change in the future. Therefore, the aim of our study was to establish the links between the subjective glare rating (using a modified version of the de Boer scale [23]), changes in visual acuity and contrast sensitivity, and psychophysiological response (in terms of HRV, SCR, and blinking frequency) following glare from different headlamps used in currently available cars (LED modules of different photometric properties--color spectrum and cut-off line gradient--and a halogen bulb reflector) within one experimental setting. The proposed methodology can be used by researchers, car and headlamp manufacturers interested in the study of glare effects, and traffic safety, as well as in user experience studies. The methodology can be further modified by introducing other tasks for the participants to solve while they are being glared, as well as by the acquisition of other physiological signals (e.g., EEG, visual evoked potentials, etc.).