The extent to which known variations in photopigment λ(max) and optical density may affect cone ratios estimated from the spectral luminous efficiency function (LEF) was examined. LEFs were generated using L- and M-cone fundamentals, one of which had been shifted in λ(max) (± 1, 2, 4 or 6 nm) or varied in peak optical density (increased or decreased by 10, 25 or 50%). A curve-fitting program was then used to estimate the L/M cone ratios for the generated LEFs assuming standard L- and M-cone fundamentals. These modeling exercises indicate that L/M cone ratios estimated from LEFs are highly correlated with long-wave sensitivity and with known variations in L-cone λ(max). Variations in M-cone λ(max) and photopigment optical density for both cone types are also correlated with L/M cone ratios, but have much less impact on the estimated ratios.
Bieber, M. L., Kraft, J. M., & Werner, J. S. (1998). Effects of known variations in photopigments on L/M cone ratios estimated from luminous efficiency functions. Vision Research, 38(13), 1961–1966. https://doi.org/10.1016/S0042-6989(97)00302-7