Vertebrate eyes can have two types of light-sensing cells, rods and cones. Rods are responsive to light levels, but cannot distinguish colors; cones (provided there's more than one type present) can differentiate colors, but are less sensitive. Humans have rods (which we use to see in low light conditions), and three types of cones, allowing for the range of color vision we experience; red-green color-blindness involves one of our three cone types being inoperative. Chameleons have at least one more type of cone than we do, allowing vision in the ultraviolet range, and their cones are densely packed, but they completely lack the rods that are generally used for low-light vision; their night vision is considerably poorer than ours, and much, much poorer than that of nocturnal animals like cats.