Effect of window size and sunlight presence on glare

Abstract

In a direct gain or a sunlighting strategy, windows are designed to admit sunlight directly into the living space. The problem of sizing the window in this case is compounded by glare usually thought to be very high and the potentially cheerful effects caused by the direct penetration of sunlight. This study examines the effect of window size on discomfort glare in such conditions based on occupants' appraisal (perceived glare) and also by using established glare prediction algorithms (calculated glare). Further, it compares perceived with calculated glare. Glare appraisals took place in a private office room of a typical size. The results indicate that, although with only low level of statistical signifieanee, window size affects glare when the observer is facing the window and this effect is described by a bell-shape curve. From a lateral position, the effect of window size is rather insignificant. The size of sunspots in the room does not affect significantly perceived glare. Furthermore, perceived glare is much lower than that derived by calculations. The factors causing such higher glare tolerance are discussed.