The Influence of Stimulus Duration on Discomfort Glare for Persons With and Without Visual Correction

Abstract

This study was concerned with the influence of the type of visual correction, duration of a stimulus, and illuminance from a stimulus on discomfort glare in nighttime traffic. The laboratory setup simulated a nighttime driving situation with an opposing glare source in the near visual periphery. There were 25 different glare stimuli, obtained by combining each of 5 levels of duration (ranging from 0.125 to 2 sec) with each of 5 levels of illuminance (ranging from 0.5 to 8 lx). There were two groups of participants: those needing no visual correction and those needing correction and having both contact lenses and spectacles. The latter group of participants used their contact lenses in ½ of the trials and their spectacles in the other ½ of the trials. Discomfort glare was evaluated using the de Boer discomfort-glare scale. Participants reported approximately the same level of discomfort glare whether they wore their contact lenses or their spectacles. In addition, although there was a tendency for persons with visual correction to report more glare than persons without correction, this effect failed to reach statistical significance. When averaged across all participants, both duration and illuminance had statistically significant effects on discomfort glare, although participants' discomfort judgments were less affected by duration than by illuminance. Both relations were well described by log-linear functions. Using these 2 functions, we generated predictions about the changes in duration and illuminance with equivalent effects on discomfort glare. For example, a 25% reduction in duration is predicted to be functionally equivalent to an 11% reduction in illuminance. These findings imply that to minimize discomfort glare in nighttime traffic it is more important to control peak illuminance than duration, at least for brief elevations in illuminance.