Cone cells, or cones, are one of the two types of photoreceptor cells that are in the retina of the eye which are responsible for color vision as well as eye color sensitivity; they function best in relatively bright light, as opposed to rod cells that work better in dim light. Cone cells are densely packed in the fovea centralis, a 0.3mm-diameter rod-free area with very thin, densely packed cones which quickly reduce in number towards the periphery of the retina. There are about six to seven million cones in a human eye and are most concentrated towards the macula.