On the calibration of high dynamic range photography for luminance measurements in indoor daylit scenes

This article describes a study of two issues concerning the calibration of high dynamic range (HDR) photography for luminance measurements in indoor daylit spaces: (i) the selection of a target in a scene for calibration and (ii) the variation of the calibration factor with different daylight levels. Luminance measurements of coloured and grey targets were conducted in a classroom under stable sky conditions using a calibrated luminance meter and HDR photography. Comparisons between luminance values measured by HDR photography and the spot luminance meter were carried out. This study affirms the findings of a previous study that grey targets are more suitable for use in the calibration of HDR photography for luminance measurements. Using a grey surface of 18% reflectance, the ratio between luminances obtained by the two methods, regarded as the calibration factor, was computed. It was found that there was a weak and insignificant correlation between calibration factor and daylight levels within the range of investigation in this study.Department of Building Services Engineerin