Discomfort glare is the annoyance, or temporary discomfort produced by luminance (brightness) within the visual field that is sufficiently greater than the luminance to which the eyes are adapted. Both small and large source glare formulae are often poor predictors of the subjective assessment of discomfort glare and, in particular, Hopkinson's daylight glare formula. This suggests that window glare depends on more factors than the four embodied in the glare calculation: source luminance, source size, surround luminance and a position index. Several studies have suggested that interest in the glare source may reduce discomfort glare in various cases. This thesis investigated a general hypothesis that an increase in interest in a glare source is associated with a decrease in discomfort glare. The investigations were performed in two main parts aiming to test the effect of interest in two cases of glare sources, a small projected screen image and a window. Indeed, a main focus of the thesis was to explore the effect of interest in the case of a window with a hypothesis that an increase in interest in a view is associated with a decrease in discomfort glare from windows. However, due to difficulty in settings and revealing the observed effect in real daylighting situations, this thesis began to see the effect of interest in the case of a small projected screen image under a highly controlled laboratory with a hypothesis that an increase in image interest is associated with a decrease in discomfort glare. The findings of this thesis tended to support the general hypothesis. It has been found that an increase in interest in a glare source is associated with a decrease in the glare discomfort, both for a small projected screen image and a window. In addition to the interest effects, significant effects of the glare source luminance variations (RML) and some characteristics and contents in a glare source were also found in both cases of glare sources.