How can I compute cone contrast of chromatic VEP stimuli (red-green and blue-yellow) on an Espeon system (Diagnosys LLC) if I know CIE 1931 coordinates and mean luminance of the stimulus:

Red (X=0.59; Y=0.35)

Green (X=0.36; Y=0.55)

Blue (X=0.20; Y=0.13)

Yellow (X=0.37; Y=0.35)

Mean luminance 14 cd/m2 ??