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Rods and cones are located in the retina in the eye. They are the eyes photo receptors. Light is picked up by the rods and cones and interpreted and sent out the optic nerve to the brain where it is interpreted and recognized. Most cones are located closer to the fovea while rods are located all over the retina. There are many more rods then cones. About one hundred thirty million rods cover the retina while only about seven million cones cover the retina.

This relationship is particularly interesting because rods and cones detect different types of light. Rods do not detect color, they can only detect black and white and shades of gray, rods are more sensitive to light and work better at night. Cones are responsible for detecting colors. The reason you can't see at night is because your cones are not able to see without a lot of light. What is interesting here is how the different levels of rods and cones affect vision. Rods and cones both have protiesn in them that allow them to sense light, these proteins are called opsin. Human have three different kinds of cones each type for one of the primary colors, red, blue and yellow. The different types of cones all have different opsin's that allow them to pick up different types of light. Rod have thinner and outer segment. The end of a rods outer segment is flatter and is not cone shaped like outer segment of a cone. The outer segment of a cone is wider and slopes inward from the bottom like a cone.