Cones Influence Color Perception

Your retina has two different types of cells that detect and respond to light—rods and cones. These cells that are sensitive to light are called photoreceptors. Rods are activated when you’re in low or dim light. Cones are stimulated in brighter environments. Most of us have about 6 million cones, and 110 million rods. Cones contain photo pigments, or color-detecting molecules. Humans typically have three types of photo pigments—red, green and blue. Each type of cone is sensitive to different wavelengths of visible light. In the daytime, a lemon’s reflected light activates both red and green cones. The cones then send a signal along the optic nerve to the visual cortex of the brain. The brain processes the number of cones that were activated and the strength of their signal. After the nerve impulses are processed, you see a color— in this case, yellow.

In a darker environment, the light reflected by the lemon would stimulate only the eyes’ rods. If only the rods are activated, you don’t see color, just shades of gray. Your past visual experiences with objects also influence your perception of color. This phenomenon is known as color constancy. Color constancy ensures that the perceived color of an object stays about the same when seen in different conditions. For example, if you looked at a lemon under a red light, you likely would still perceive the lemon to be yellow.