High-Dynamic Range Imaging (HDMI) as Validation and Design Tool in Assessing Daylight Discomfort Glare

As glass facades become prevalent in our cities, daylighting -- with the dual goals of energy savings and occupant amenity -- is identified as a major driver. Performance metrics traditionally used to evaluate electrical lighting design, such as illumination levels, are proving to be less useful for evaluating visual comfort performance in a highly glazed situation. Discomfort glare in a daylighted space has a large impact on occupant comfort, but it has been difficult to predict during the design process. A host of glare indices have been developed to address this need, but the validation of these indices for daylighting is still underway. Today, many designers use rules of thumb for luminance ratios. RADIANCE software can predict luminance conditions and produce predicted luminance maps used for visual comfort evaluation. The development of High Dynamic Range photography calibrated for luminance levels can produce similar luminance maps from photographs of existing spaces. This tool closes the loop between prediction and validation. Using recently constructed projects, this paper describes the use of post-occupancy HDRI in the validation of luminance predictions as well as the use of calibrated HDRI and predictive simulations in the design phase.

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