Excel calculator, please cite: David, Aurelien, Fini, Paul T., Houser, Kevin W., Ohno, Yoshi, Royer, Michael P., Smet, Kevin A. G., . . . Whitehead, Lorne. (2015). Development of the IES method for evaluating the color rendition of light sources. Optics Express, 23(12), 15888-15906. doi: 10.1364/OE.23.015888
More information on the importance of the proposed updates to the CIE Ra can be found in: Smet, Kevin A.G., David, Aurelien, & Whitehead, Lorne. (2016) “Why color space uniformity and sample set spectral uniformity are essential for color rendering measures,” LEUKOS, vol. 12, no. 1–2, pp. 39–50. doi: 10.1080/15502724.2015.1091356