Improved color fundamentals offer a new view on photometric additivity

New action spectra are derived for the foveal cones on the basis of three assumptions: (1) the Stiles-Burch (1959) colorimetric data are better than CIE 1931; (2) the long wavelength flanks of the dichromatic luminosity functions offer better anchorage than the confusion loci; and (3) the relative mutual heights per receptor can be derived from the Bezold-Brücke effect. Since these assumptions do not include photometric data, we could at the end ask how L lambda, M lambda and S lambda combine to V lambda. The best answer appeared to be V lambda = 0.68 L lambda + 0.34 M lambda -0.02 S lambda, reflecting both relative receptor population densities and a negative input of the S-system to luminance.