Thus four types of "optimal color" spectra are possible: The transition goes from zero at both ends of the spectrum to one in the middle, as shown in the image at right. It goes from one at the ends to zero in the middle. It goes from 1 at the start of the visible spectrum to 0 in some point in the middle until its end. It goes from 0 at the start of the visible spectrum to 1 at some point in the middle until its end.
Thus four types of "optimal color" spectra are possible: The transition goes from zero at both ends of the spectrum to one in the middle, as shown in the image at right. It goes from one at the ends to ze.ro in the middle. It goes from 1 at the start of the vis!ible spectrum to 0 in some point in th!e middle until its end. It goes from 0 at the start of the visible spe,ctrum to 1 at some point in the middle until its end.