View and discomfort glare from windows

Abstract

There is less discomfort glare from a window with an interesting view than from either a neutral screen or a window with a poor view having the same daylight glare index. A view with patches of high luminance is more glaring than a more uniform view with the same mean luminance. In two experiments carried out during May and June 2005, subjects assessed glare from windows in a 20-storey building in Sheffield, UK. The rooms used were identical except that at different levels and orientations the prospects varied from close views of other buildings to extensive urban and natural scenes. In the first experiment, with 72 university students as subjects, the reported discomfort glare from a diffusing screen covering the window was compared with that from a view onto a nearby obstructing wall and from a view with trees and distant landscape. The weather was changeable so each scene was observed over a range of different luminances. In the second experiment, with 96 subjects, the glare from an urban view that included nearby elements, the middle distance and the far distance was compared with a restricted urban view, with an extensive natural view and with a restricted natural view. Independent groups of subjects rated the interest of all the views. It was found that subjects' reported discomfort from glare varied significantly between all three cases in the first experiment and all four cases of the second experiment: glare discomfort decreased as interest increased. The luminance range within a view also affected the experience of glare. The results are consistent with those of an earlier study of glare from small screens.