Methods for evaluating discomfort glare
Previous research has found that the de Boer scale--the most frequently used discomfort glare scale in the automotive context--is not compatible with population sterotypes of U.S. observers. Consequently, when used, the de Boer scale is often made continuously visible to the observers. The present study was designed to compare the rating obtained from the de Boer scale to ratings from three alternative discomfort glare scales. Of additional interest was the relation between discomfort glare ratings and brightness ratings for the same stimuli. the scales evaluated were the de Boer scale, the DANDY scale (a newly developed categorical scale), an anchored magnitude estimation scale, a free magnitude estimation scale, and a brightness magnitude estimation scale. There are two main findings. First the discomfort ratings from the four tested discomfort glare scales were highly intercorrelated. Second, brightness ratings from a magnitude estimation scale were highly correlated with ratings from an analogous discomfort glare scale. An implication of these findings is that brightness ratings provided essentially the same information as discomfort ratings using any of the four tested discomfort glare scales. Consequently, to the extent that brightness is a concept that is easier to communicate to subjects than is discomfort, researcher interested in discomfort glare might consider using brightness scales.