The spectrum on the right details the UV-Vis absorption chatacteristics of : retinal, free and bound as rhodopsin.
There are four kinds of rhodopsin in
the human eye each of which has retinal
absorbing at a different wavelength.
Vision is an animation detailing the chemical basis of Visible light absorption in the retina (courtesy of the Archipelago technology company).
Rhodopsin is an animation detailing tertiary structure of the protein Rhodopsin , with the retinal shown in red (courtesy of the Wison Research group , at UCSD).