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Abstract
New research in daylighting metrics and developments in validated digital High Dynamic Range (HDR) photography techniques suggest that luminance based lighting controls have the potential to provide occupant satisfaction and energy saving improvements over traditional illuminance based lighting controls. This paper studies occupant preference and acceptance of patterns of luminance using HDR imaging and a repeated measures design methodology in a daylit office environment. Three existing luminance threshold analysis methods [method1: predetermined absolute luminance threshold (for example, 2000 cd/m2), method2: scene based mean luminance threshold and method3: task based mean luminance threshold] were studied along with additional candidate metrics for their ability to explain luminance variability of 18 participant assessments of ‘preferred’ and just disturbing' scenes under daylighting conditions. Per-pixel luminance data from each scene were used to calculate Daylighting Glare Probability (DGP), Daylight Glare Index (DGI), and other candidate metrics using these three luminance threshold analysis methods. Of the established methods, the most consistent and effective metrics to explain variability in subjective responses were found to be; mean luminance of the task (using method3; adjr2 = 0.59), mean luminance of the entire scene (using method2; adjr2 = 0.44), and DGP using 2000 cd/m2 as a glare source identifier (using method1; adjr2 = 0.41). Of the 150 candidate metrics tested, the most effective was the ‘mean luminance of the glare sources’, where the glare sources were identified as 7* the mean luminance of the task position (adjr2 = 0.64). Furthermore, DGP consistently performed better than DGI, confirming previous findings. ‘Preferred’ scenes never had more than ∼ 10 percent of the field of view (FOV) that exceeded 2000 cd/m2. Standard deviation of the entire scene luminance also proved to be a good predictor of satisfaction with general visual appearance.