Rod cell Rod cell Rod cells are photoreceptor cells in the retina of the eye that can function in less intense light than the other type of visual photoreceptor, cone cells. Rods are usually found concentrated at the outer edges of the retina and are used in peripheral vision. On average, there are approximately 90 million rod cells in the human retina. Rod cells are more sensitive than cone cells and are almost entirely responsible for night vision. However, rods have little role in color vision, which is the main reason why colors are much less apparent in dim light, and not
Von Kries coefficient law von Kries coefficient law built upon theories and research done by Hermann von Helmholtz. A German physicist and physician, Helmholtz asserted that “the nervous substance in question is less sensitive to reacting light falling on it than the rest of the retina that was not previously stimulated”. Helmholtz, along with Thomas Young, proposed the trichromatic theory, or the Young–Helmholtz theory, that stated that the retina contains three types of cones, which respond to light of three different wavelengths, corresponding to red, green, or blue. Activation of these cones in different combinations and to different degrees results in the perception of