How can animals see at night?

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Animals have developed several adaptations that allow them to see at night. These adaptations vary among species, but they generally involve structural and physiological changes in the eyes and the way the brain processes visual information.
  1. Large Eyes and Pupils: Many nocturnal animals, such as owls and cats, have large eyes and pupils that can open wide to allow more light to enter the eye. This helps them make the most of the limited light available at night124.
  2. Tapetum Lucidum: This is a mirror-like layer located behind the retina in many nocturnal animals. It reflects light that passes through the retina, giving the retinal cells a second chance to sense it. This is why some animals' eyes shine in the glare of car headlights124.
  3. Rods and Cones: The retina contains two types of light-sensing cells: rods and cones. Rods can sense very dim, scattered light, but don't produce a color image, while cones account for color vision but require bright, focused light. Nocturnal animals have retinas packed with rods and fewer cones, allowing them to see in low light conditions, albeit with less color and detail124.
  4. Specialized Rod Cells: In nocturnal animals, the densest material is in the center of the rod cell nucleus, effectively focusing all of the available light in one area. This adaptation helps them make the most of the limited light available at night12.
  5. Head Rotation: Some animals, like owls and tarsiers, can rotate their heads to a large degree (up to 270 degrees for owls and 180 degrees for tarsiers) to compensate for their inability to rotate their large, tubular eyes in their sockets124.
  6. Thermal Vision: Some animals, like snakes, rely less on rods in their retinas and more on thermal vision, which lets them see the body heat of nearby mammals5.
  7. Bioluminescence: In the deep sea, where little or no sunlight penetrates, many animals have developed the ability to produce their own light through a chemical reaction known as bioluminescence. This light is used for various purposes, including attracting or finding prey, scaring off or avoiding predators, and finding mates5.
It's important to note that while these adaptations enhance night vision, they do not provide perfect vision in complete darkness. Even nocturnal animals aren't active in the darkest hours of a moonless night1.
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