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.