Photoreception

photoreception, any of the biological responses of animals to stimulation by light.

In animals, photoreception refers to mechanisms of light detection that lead to vision and depends on specialized light-sensitive cells called photoreceptors, which are located in the eye. The quality of vision provided by photoreceptors varies enormously among animals. For example, some simple eyes such as those of flatworms have few photoreceptors and are capable of determining only the approximate direction of a light source. In contrast, the human eye has 100 million photoreceptors and can resolve one minute of arc (one-sixtieth of a degree), which is about 4,000 times better than the resolution achieved by the flatworm eye.

The following article discusses the diversity and evolution of eyes, the structure and function of photoreceptors, and the central processing of visual information in the brain. For more information about the detection of light, see optics; for general aspects concerning the response of organisms to their environments, see sensory reception.