Quantitative assessment of commercial filter 'aids' for red-green colour defectives

The claims made for 43 commercial filter ‘aids’, that they improve the colour discrimination of red‐green colour defectives, are assessed for protanomaly and deuteranomaly by changes in the colour spacing of traffic signals (European Standard EN 1836:2005) and of the Farnsworth D15 test. Spectral transmittances of the ‘aids’ are measured and tristimulus values with and without ‘aids’ are computed using cone fundamentals and the spectral power distributions of either the D15 chips illuminated by CIE Illuminant C or of traffic signals. Chromaticities (l,s) are presented in cone excitation diagrams for protanomaly and deuteranomaly in terms of the relative excitation of their long (L), medium (M) and short (S) wavelength‐sensitive cones. After correcting for non‐uniform colour spacing in these diagrams, standard deviations parallel to the l and s axes are computed and enhancement factors El and Es are derived as the ratio of ‘aided’ to ‘unaided’ standard deviations. Values of El for traffic signals with most ‘aids’ are