Photoreceptors are photosensitive neurons in the outer part of the retina. In a process known as phototransduction, photoreceptors convert light information into electrical signals. Visual pigments in photoreceptor outer segments absorb incident photons and initiate a series of specific and complex biochemical reactions that change the membrane potential of the cells. This information is used by the visual system to form a complete representation of the visual world. In vertebrates, there are two types of photoreceptor cells: cones and rods. Cones are adapted to detect fine detail, central and colors vision and function well in bright light. Rods are responsible for peripheral and dim light vision. The number and ratio of rods to cones varies among animals, dependent on whether the animal is primarily diurnal or nocturnal.