It took me some time to understand why #1 and #3 are metamers but I think it has to do specifically with the fact that there just isn't a lot of sensitivity on S, M, or L for wavelengths around 650nm, at least not enough to make a difference. But this also kind of raises an interesting challenge, what are some spectra that would be metamers for (suppose) aliens with different sensitivities than us, but not metamers for humans? How could you calculate that?
It took me some time to understand why #1 and #3 are metamers but I think it has to do specifically with the fact that there just isn't a lot of sensitivity on S, M, or L for wavelengths around 650nm, at least not enough to make a difference. But this also kind of raises an interesting challenge, what are some spectra that would be metamers for (suppose) aliens with different sensitivities than us, but not metamers for humans? How could you calculate that?