Discomfort glare under automotive conditions – spectral behavior and mechanisms

A new experimental apparatus was constructed to study the spectral behaviour of discomfort glare and to explore its visual mechanisms. The apparatus includes two quasi-monochromatic optical channels to project quasi-monochromatic and quasi-bichromatic glare stimuli. Observation geometries and luminance levels address the practical application of automotive headlamps. To model oncoming automotive headlamps, a typical angular size of =0.1° was chosen on a typical background luminance of LB=0.1 cd/m2 and at a typical retinal eccentricity of =4.3° to the left of the fixation point where car headlamps tend to appear. The value of =0° has also been considered for comparison. The de Boer value of 5 (just admissible) was chosen which is relevant for night time traffic and easy to set by the observer by adjusting a neutral density filter wheel. The apparatus consists of two interference filter wheels (10 nm HBW) constituting two optical channels each producing a quasi-monochromatic beam from the two Xenon short arc high-pressure lamps, a beam splitter to unite the two channels to produce a quasi-bichromatic beam. The glare source is a changeable 0.1°-0.5° aperture inside a glare observation booth illuminated by four dimmable white LEDs. The device is calibrated by a spectroradiometer looking into the booth and measuring spectral radiance at a white standard at the position of the subject’s left eye. Discomfort glare results have shown effects of both additive and opponent cone mechanisms. Opponent cone mechanisms e.g. |L-M| cause spectral non-additivity to be predicted by a new discomfort glare model. Due to the mesopic surround, the rod effect cannot be excluded