Band Systems for Appraisal of Color Rendition

Chromaticity shifts on the RUCS scale, for 20% increase in intensity in a single band 0.01 μ wide, were computed for deluxe cool-white and warm-white fluorescent lamps and ten hypothetical pigments with color points almost uniformly spaced about that of the illuminant. At each wavelength, the color shift of the most sensitive pigment was taken as a measure of the importance of the spectral flux per 100 A. Seven bands of roughly equal importance in rating cool-white lamps have division points at 0.44, 0.49, 0.53, 0.56, 0.60, and 0.62 μ. For warm-white lamps, the second division point listed above should be omitted. The outer limits of the end bands should be 0.42 and 0.67 μ for ratings based on unweighted energy flux. For comparisons of dissimilar spectral curves, one should weight energy flux within each band in proportion to the maximum shift on the RUCS scale, per unit increment of spectral flux. This weighting factor has maxima at approximately 0.445, 0.53, and 0.615 μ and minima at 0.49 and 0.57–0.58 μ.Importance in rating deluxe cool-white lamps is only 5 and 8, respectively (average=100) for Bouma’s end bands, 51–195 for the other six, and 73–136 for Kruithof’s 7-band system.