Despite nearly a century of research, we are still unable to accurately predict discomfort due to glare.
The vast majority of discomfort glare research uses subjective evaluations – primarily category rating or luminance adjustment. This article discusses methodological issues which contribute to uncertainty in evaluations.
Evaluations of discomfort using category rating were compared against involuntary physiological responses.
Subjective evaluation of discomfort was highly correlated with eye movement and pupil constriction: Severe glare discomfort increased the speed of eye movement and caused larger pupil constriction.
A series of experiments were conducted to explore the influence of variations in experimental design, the aim being to explain the variance between different studies.
In this first experiment we explored the influence of anchor bias in luminance adjustments.
Kent M, Fotios S, Altomonte S. Discomfort glare evaluation: The influence of anchor bias in luminance adjustments. Lighting Research and Technology. First Published October 13, 2017. doi.org/10.1177/1477153517734280.
When Hopkinson used his multiple criterion scale, test participants used adjustment to set the luminance representing a defined degree of discomfort. One limitation was that the four degrees of discomfort were evaluated only in ascending order.
In this experiment we repeated Hopkinson’s method but also using descending and randomised orders of discomfort. The different orders led to significant differences in luminance for a given degree of discomfort.
When evaluating discomfort the test participant must look somewhere, and for evaluating discomfort from peripheral sources a fixation task is used. This experiment compared the use of a simple fixation mark and a task requiring a degree of cognitive attention. The results confirmed a lower degree of discomfort is expressed when engaged in a task demanding a higher degree of cognitive attention.
Winter J, Fotios S, Völker S. The effects of glare and inhomogeneous visual fields on contrast detection in the context of driving. Lighting Research and Technology. first published on October 7, 2016 as doi:10.1177/1477153516672719.
Further articles have been submitted which investigate the influence on discomfort evaluations of showing a pre-trial demonstration of the stimulus range, and of the bias induced by stimulus range itself.