Estimating Melatonin Suppression and Photosynthesis Activity in Real-World Scenes from Computer Generated Images

In lighting design and architectural illumination planning simulations of luminance and illuminance distributions within scenes are performed using rendering tools such as RADIANCE. In this paper we focus on the evaluation by two action spectra other than the luminous efficiency function – the circadian action function describing the melatonin suppression and the photosynthesis action function. We show how indices that are derived from these action spectra can be calculated from spectrally rendered images of a real-world scene. For both action spectra we derive approximations based on the CIE color matching functions that allow estimations of the corresponding index from RGB rendered images. We evaluate the differences between the spectral results and the RGB approximations for an office room with three different types of illumination. Background Physically based rendering packages such as RADIANCE are used in lighting design and architectural illumination planning for simulations of luminance and illuminance distributions. Especially for daylight simulations and daylight factor calculations this rendering tool is widely used and was shown to be accurate in [1, 2, 3]. However, spectral rendering is necessary if highly accurate results are desired as for example color shifts may occur when calculations are performed in the RGB color space [4, 5]. In the present study not only the CIE photopic luminous efficiency function V(λ) that is used to calculate (il)luminances from (ir)radiances and which equals the CIE color-matching funtion ¯ y [6], but also other weighting functions are considered. In detail, two action spectra are used for evaluations in a real-world test scene: the circadian action function describing the melatonin suppression and the photosynthesis action spectrum representing a plant’s photosynthesis activity. Circadian action function The hormone melatonin, which is mainly secreted during the night, is primarily responsible for the regulation of the circadian rhythm. Light in general and radiation in the blue part of the visible spectrum in particular suppresses the secretion of this hormone. Gall [7] defines a circadian action function c(λ) that is based on experimental data from Brainard [8] and Thapan [9] for light-induced melatonin suppression. The spectral distribution of c(λ) is shown in Figure 1. Using this circadian action function, Gall calculates the circadian radiation quantity Xec, which we refer to asC, by