a theory that the perception of color relies on the activation of three types of cells: (a) scotopic dominators, which are retinal rods most sensitive to wavelengths of 500 nm; (b) photopic dominators, which are retinal cones most sensitive to wavelengths of 560 nm; and (c) photopic modulators, other cones sensitive to very narrow frequency ranges. [Ragnar Arthur Granit (1900–1991), Finnish-born Swedish physiologist]