Psyb51- chapter 5 the perception of color| page1. The fact that an infinite set of different wavelength intensity combinations can elicit exactly the same response from a single type of photoreceptor. One photoreceptor type cannot make color discriminations based on wavelength. Explains the lack of color in dimly lit scenes. Light intensities that are bright enough to stimulate the rode receptors but too dim to stimulate the cone receptors. All rods are sensitive to low light levels. All rods contain the same type of photopigment molecule: rhodopsin = same light sensitivity to wavelength. Light intensities that are bright enough to stimulate the cone receptors and bright enough to saturate the rod receptors i. e. drive them to their maximum responses). Cones come in three varieties contain a different photopigment. With the three cone types we can tell the diff b/w lights of diff wavelengths, b/c this produces a unique set of 3 response from the three cone types.