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96 <br />Factors Affecting the Perception of Glare <br />I. Introduction <br />U. Situation Factors that Affect the Perception of Glare <br />III. Human Factors that Affect the Perception of Glare <br />L Introduction <br />Glare can be defined as any brightness that causes a viewer discomfort, interference with vision, or <br />eye fatigue. The sensation of glare occurs when the brightness (luminance) of an object is <br />significantly higher than the brightness to which the eye is currently adapted. The severity of the <br />sensation of glare experienced by a viewer is dependent on a number of factors relating to the glare <br />source(s) and the viewer. <br />U. Situation Factors that Affect the Perception of Glare <br />A. Brightness (luminance) of the Glare Source <br />The severity of the glare sensation depends on the brightness of the glare source. The <br />human eye can adapt to a wide range of luminance, so small changes in luminance are not <br />noticeable. Generally speaking, the illuminance of an object must be doubled or halved in <br />order to significantly affect the perceived glare from that object. <br />B. Size of the Glare Source <br />The severity of the glare sensation depends on the size of the glare source. The greater a <br />portion of the field of view that is occupied by the glare source, the greater the sensation of <br />glare will be. The size of a glare source can be expressed mathematically as the solid <br />angle it fills. <br />For sports lighting, an entire light bank is often perceived as a single light source. Thus, it <br />is generally desirable to have several small light banks as opposed to a few large light <br />banks, so that individually light banks cause less glare sensation. <br />C. Position of the Glare Source <br />The severity of the glare sensation depends on the position of the glare source within the <br />field of view. The closer the glare source is to the viewing direction, the more severe the <br />glare sensation. For sports lighting, the position of the glare source is a key design <br />element. Use of proper pole locations and heights ensures that the position of floodlights is <br />not in the primary viewing directions of players. Likewise, it is important to consider the <br />position of light poles relative to nearby roads or intersections. <br />D. Brightness Contrast and Eye Adaptation <br />The severity of the glare sensation depends on the brightness contrast of the glare source to <br />the surroundings. The human eye adapts to the average brightness of the field of view by <br />800 825 6030 <br />WWW.musco.com <br />email: lighting @musco.com <br />0 2001 Musco UghHng Page 1 of 2 <br />