Uncertainty in subjective evaluation of discomfort glare

The magnitude of discomfort glare has often been evaluated using the de Boer rating scale. This note raises doubts about measuring discomfort glare this way. There is a possibility that the presence of discomfort may be a false alarm because this rating scale forces an opinion and/or because the response scale does not include a `no glare' option. Further, there is a possibility that response variance is increased through uncertainty over the meaning of the magnitude descriptors. Actions that will reduce the likelihood of such distortions occurring are suggested.