The mechanism behind the discomfort glare phenomenon, the kind of glare provoking an irritating or distracting effect, is not well understood. Since some of the factors influencing this phenomenon are still unknown, no current indices can properly explain the high variability existing between individuals' discomfort glare perception. A list of potential factors influencing the degree of perceived discomfort glare in daylighting has been established from existing literature. In addition to the physical quantities commonly used in glare indices, other variables, whether psychological, physiological, related to light or to the context, could influence the degree of perceived discomfort glare. (C) 2017 The Authors. Published by Elsevier Ltd.