Is Exterior Glare Problematic? Investigation on Visual Discomfort Caused by Reflected Sunlight on Specular Building Facades

Highly reflective and specular building envelopes have been widely adopted to help maximize energy performance of buildings and to achieve occupant thermal and visual comfort. This strategy has ensured these benefits inside the building envelope while making a significant and sometimes unintended impact outside the building envelope. Reflected sunlight from specular building envelopes can cause discomfort glare to people outside buildings. It is important to investigate exterior glare issues caused by specular material characteristics. This often parallels, but is distinct from, thermal issues resulting from radiant gain. Preliminary exterior glare scene documentations were performed in downtown Los Angeles to understand existing problems. Human subject study was performed in an outdoor research setting. High dynamic range (HDR) imaging was used to capture and evaluate different levels of scenes and to visualize glare sources in the field of view. Collected subjective evaluation data and captured glare scenes were statistically analyzed to prove the existence of exterior glare problems. Perceptible and disturbing glare levels were experienced by the subjects, and strong correlations were found between human visual discomfort and excessive sunlight reflections from specular building envelopes.