In this paper, the potential, limitations and applicability of the High Dynamic Range (HDR) photography technique are evaluated as a luminance mapping tool. Multiple exposure photographs of static scenes were taken with a commercially available digital camera to capture the wide luminance variation within the scenes. The camera response function was computationally derived by using Photosphere software, and was used to fuse the multiple photographs into an HDR image. The vignetting effects and point spread function of the camera and lens system were determined. Laboratory and field studies showed that the pixel values in the HDR photographs correspond to the physical quantity of luminance with reasonable precision and repeatability.

Existing visual comfort metrics are reviewed and critiqued based upon their ability to explain the variability in human subjective responses in a daylit private office laboratory environment. Participants (n = 48) evaluated visual comfort and preference factors, totaling 1488 discreet appraisals, and luminance-based metrics were captured with high dynamic range images and illuminance-based metrics were recorded. Vertical illuminance outperformed all commonly referenced visual comfort metrics including horizontal illuminance, IES luminance ratios, daylight glare probability (DGP), and daylight glare index (DGI). The bounded borderline between comfort and discomfort is introduced, and preliminary visual comfort design criteria are proposed for several existing metrics. Fundamental limitations of glare indices are documented, and the implications of inconsistent application of luminance ratio calculation methods are quantified. Future research is detailed.

The human ocular system functions in a dual manner. While the most well-known function is to facilitate vision, a growing body of research demonstrates its role in resetting the internal body clock to synchronize with the 24-hour daily cycle. Most research on circadian rhythms is performed in controlled laboratory environments. Little is known about the variability of circadian light within the built and natural environments. Currently, very few specialized devices measure the circadian light, and they are not accessible to many researchers and practitioners. In this paper, tristimulus colour calibration procedures for high dynamic range photography are developed to measure circadian lighting. Camera colour accuracy is evaluated through CIE trichromatic (XYZ) measurements; and the results demonstrate a strong linear relationship between the camera recordings and a scientific-grade colorimeter. Therefore, it is possible to correct for the colour aberrations and use high dynamic range photographs to measure both photopic and circadian lighting values. Spectrophotometric measurements are collected to validate the methodology. Results demonstrate that measurements from high dynamic range photographs can correspond to the physical quantity of circadian luminance with reasonable precision and repeatability. Circadian data collected in built environments can be utilized to study the impact of design decisions on human circadian entrainment and to create guidelines and metrics for designing circadian friendly environments.

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