Human perceptions of daylight composition in architecture: a preliminary study to compare quantitative contrast measures with subjective user assessments in HDR renderings

Humans perceive daylight as a rich and dynamic luminous composition and yet existing performance metrics most often evaluate natural illumination for its ability to adequately illuminate a two-dimensional task surface while avoiding glare-based visual discomfort. This rather limited task-driven approach places a disproportionate emphasis on surface illumination and glare-based discomfort and ignores the likelihood that contrast can provide a positive visual impact on our impression of space. Existing studies on perceptual daylight performance have linked subjective ratings to digital images, yet they have relied on simple global contrast measures without reaching a robust consensus. These ‘global’ measures do not account for the composition of luminance values within a scene and while more robust methods have been developed in computational graphics, vision research, and psychology, they have not been applied to studies in qualitative lighting research. As daylight-driven visual effects in daylit space are heavily influenced by dynamic sky conditions, this paper will introduce an experimental method for comparing subjective ratings of daylight composition in architecture against existing global and local contrast metrics under a range of annual moments. The goal of this paper is to identify which quantitative measures (local and/or global contrast metrics), if any, correlate to subjective responses for contrast, uniformity, complexity, variation, stimulation, and excitement. This preliminary study will test which factors: sky type, spatial composition, or subject, shows a significant effect on these ratings.