Cone cells or simply cones are special photoreceptor cells in the retina. They react to light and work best in relatively bright light. Cone cells are less sensitive to light that rod cells. Human eyes usually have different types of cone cells. This makes it possible to distinguish different colors. Rod cells are more sensitive to light, but cannot tell colors apart. In a publication done in 1935, Osterberg thinks that there are about 6 million cone cells in a human eye.
That way, cones allow to tell colors apart. Their reaction to stimuli is faster than that of the rod cells. For this reason, they can perceive finer details, and more rapid changes in images. Because humans usually have three kinds of cones, with different photopsins, which have different response curves, and thus respond to variation in color in different ways, they have trichromatic vision. Being color blind can change this, and there have been reports of people with four or more types of cones, giving them tetrachromatic vision.
- G. Osterberg (1935). “Topography of the layer of rods and cones in the human retina,” Acta Ophthalmol., Suppl. 13:6, pp. 1–102.
- Kandel, E.R.; Schwartz, J.H, and Jessell, T. M. (2000). Principles of Neural Science (4th ed. ed.). New York: McGraw-Hill. pp. 507–513.