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In the eye
Light from external objects enters the eye through the pupil. The human eye has a lens and iris diaphragm which serve similar functions to the corresponding features of a camera. The optics of the eye form an upside-down image of those objects on the rear, inner surface of the eyeball (the retina). There, a dense carpet of light sensitive photoreceptors converts light (photons) into electro-chemical signals, which are processed by neural circuits in the retina and transmitted to the brain.
The retina contains two types of photoreceptors, rods and cones. The rods, located in the peripheral retina, give us our night vision, but can not distinguish color. Cones, located in the center of the retina (called the macula), are not much good at night but do let us perceive color during daylight conditions.
Our visual system provides a motion sensor system with nearly 180 degrees horizontal coverage. The eye's peripheral vision system only supports low resolution imaging but offers an excellent ability to detect movement through a wide range of illumination levels. This motion detection has been useful to human kind for protection from aggressors and for spotting game while hunting. The retina is the thin layer of nerve cells. The majority of the eye's inside chamber has this retina layer, accounting for the very wide angle of our peripheral vision.
The eye's high resolution color vision system has a much narrower angle of coverage. Our high resolution vision can adapt to widely varying illumination colors and levels. This system evolved primarily as a daylight system and ceases to work well at very low illumination levels. This is why our vision is typically blurry if it is very dark. The sensors associated with this system are concentrated around the eye's fovea. The light sensor cells capable of working over a wide illumination levels and of providing quick response to changes are called rods. High resolution color imaging is provided by light sensor cells called cones.