A proper glare prediction method is needed to promote visual comfort. The purpose of this study is to suggest the methodology to identify the glare source, which is necessary in order to control glare coming from windows. Experiments with subjects were conducted in order to evaluate discomfort glare from windows and the features that made the subjects recognize the glare sources in the windows with non-uniform luminance distributions were explored. Discomfort glare was evaluated in two categories: first across the whole window and then by unit area of the window. The results of the evaluations led to the realization that the discomfort glare value of the whole window is larger than the mean value of the discomfort glares from the window patches. In addition, it is revealed that the evaluated value of discomfort glare is a function of the average luminance of the visual field. There is a linear relationship between the average luminance of the visual field and the average luminance of the glare patches. Such linear relationship has been translated into a formula, whose high accuracy is proven in the study. Using the formula makes it possible to easily identify the window patches that would generate glare. (c) 2011 Elsevier B.V. All rights reserved.