L-opsin

The Opsin in humans that is excited by the longer Wavelengths in the Visible Range (hence the “L” for Long). The typical form has a Peak Wavelength at 570nm, which is in fact a wavelength that excites yellow in Color Normals, not the red that the opsin is usually associated with (e.g. Red Cone).

The opsin is encoded by the OPN1LW Gene on the X-Chromosome. When this gene is missing (or altered enough to be inoperative), the individual exhibits Protanopia. When this gene has a minor mutation (usually a Hybridization with the OPN1MW that shifts the opsin to shorter wavelengths, towards the M-opsin in the Absorption Spectrum), the opsin becomes the L*-Opsin, and the individual often exhibits Protanomaly.