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Abstract

The discovery of ipRGCs and the circadian effects of light that activates them has led to significant interest in the quantification of environmental illumination in physiological terms for both vision scientists and lighting industry professionals. One such tool that can be used to such an end is the Westboro Photonics ‘Circadiometer’, a five-channel, high dynamic range camera whose filters correspond to physiological receptors in the eye. Using this device, we have collected a dataset of physiologically-relevant images from a workstation in a typical office environment which can be used to give us insight into the kinds of times and spaces at which there are significant changes to circadian-affective light. Principal Component Analysis revealed that the scene was statistically divided between regions that were mainly illuminated by different sources. Regression analysis of the melanopic and luminance maps of the scene showed, predictably, very high correlations, however they also revealed regular periods of decorrelation. These periods demonstrate ‘transition periods’ wherein the light source that dominates the scene switches. These have significant implications for the availability of natural light and the operation of automatic indoor lights in shared work environments. We also discuss the feasibility of other data collection and analysis methodologies; namely, the creation of circadiometric ‘lightprobes’, which provide a panoramic measurement of light reaching one point in space.