An Approach to Predict Daylight Glare Using Nazzal’s Daylight Glare Index Formula

One of the important functions of window is to admit natural lightto interior spaces of buildings. This natural lighting in buildings helps to displace the requirement for artificial lighting, and thus, helps to save energy. Though daylight has positive effects on visual comfort, but high window luminance or direct sunlight from a window may cause discomfort. Visual discomfort in a day-lit interior environment is usually represented by the degree of discomfort glare.Only a few formulae have been proposed for discomfort glare of daylight and they are not sufficient in real daylight situations. No standard monitoring procedure is available to establish the value of daylight glare ona comparative basis. This paper introduces a new glare evaluation method proposed by Ali A. Nazzal. This method is actually modified P. Chauvel‟sglare formula.The paper aims to predict the discomfort glare from daylighting using data collected from a room having twonorth facingwindows. The Daylight Glare Index was evaluated according to different interpretations of the background luminance in the presence of daylight, and also with artificial light together. Discomfort glare from bright luminaires or windows is not a simple matter but consists of a complex relationship between a numbers of factors. In this paper the change in the discomfort glare, depending on the change in the background luminance was measured using two windows. The results showed that the higher the background luminance, the smaller the observer‟s degree of discomfort glares. Glare can therefore be reduced by cutting down the size and brightness of the visible patch of sky and by increasing the interior brightness by the judicious use of surface areas of high reflectance.