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Cats have excellent night vision and can see at only one-sixth the light level required for human vision.[65]:43 This is partly the result of cat eyes having a tapetum lucidum, which reflects any light that passes through the retina back into the eye, thereby increasing the eye`s sensitivity to dim light.[97] Another adaptation to dim light is the large pupils of cats` eyes. Unlike some big cats, such as tigers, domestic cats have slit pupils. These slit pupils can focus bright light without chromatic aberration, and are needed since the domestic cat`s pupils are much larger, relative to their eyes, than the pupils of the big cats. At low light levels a cat`s pupils will expand to cover most of the exposed surface of its eyes.[99] However, domestic cats have rather poor color vision and like most nonprimate mammals have only two types of cones, optimized for sensitivity to blue and yellowish green; they have limited ability to distinguish between red and green. From wikipedia