Evaluation of Glare Indices in Educational Buildings in Hot and Dry Climate of Iran

It is generally well-known and understood that daylight and view help to create healthy, comfortable, and productive work environments for building occupants. Human can obtain many benefits associated with daylight and view, which are one of the most important reasons to provide sufficient amount of daylight and view in buildings. The perceived value of views through daylight openings such as windows has persisted throughout time. Windows have great perceived and observable commercial value in buildings. Nevertheless, providing daylight and view in buildings should be done in a way that is acceptable to the occupants, so that a balance between energy savings and thermal/visual comfort can be achieved. There is still risk of having low level of comfort perceived by the occupants, particularly in the form of discomfort glare, which can significantly reduce energy savings. Discomfort glare occurs when the eyes have adjusted to a certain general level of brightness, and some annoying, distracting, or blinding light appears within the visual field. Glare can be described in one of three main ways: according to the process that created the glare, according to an individual's perceived degree of glare intensity, and according to the results of the glare. Although the topic of discomfort glare is an important issue in daylight buildings; however, a consensus on the glare indices and their criteria is hard to achieve, since any measured objective values must show a significant correlation with perception of the space occupants. Applicability of the criteria for each glare indices is yet to be determined, considering various demographic and cultural differences and preferences. Many researches are done in laboratory conditions or controlled environments and have not been repeated in field studies. Glare is a subjective phenomenon and many factors can affect its perception. Occupant-based factors can influence individuals’ glare perception. There is little consensus between different studies in varied space types and climates. This research aims to determine the appropriate criteria for discomfort glare in Iran, using high dynamic range (HDR) imaging technique and post-occupancy evaluation. The objectives are to find correlations between various physical variables and glare indices and to obtain the comfort criteria for day-lighting glare in Iran. This paper provides recommendations to determine discomfort glare in daylight space based on high dynamic range image and questionnaire in Iran and compares five different glare indices. Many existing glare indices including DGP (Daylight Glare Probability), DGI (Daylight Glare Index), UGR (Unified Glare Rating), VCP (Visual Comfort Probability), and CGI (CIE Glare Index) focus on evaluating perceived degree of glare intensity. For assessing these indices, a questionnaire was developed and by reviewing the HDR results and the questionnaire, it was determined which criteria is more applicable under different circumstances. It is found that DGP yields the most plausible results. UGR has the highest rate for assessing perceptible glare, DGI has acceptable accuracy for assessing imperceptible glare and the best performance of CGI is in intolerable glare scenes. VCP has the least degree of accuracy in each stage. Thus, VCP is not suitable for use in calculations of daylight glare.