Book 4, Question 128
Why Do Eyes Shine in a Flashlight?
Many night animals have a mirror layer at the back of the eye called the [tapetum, tah-PEE-tum]. Light goes in, bounces off it, and comes back out. That bounce gives the eye a second chance to catch the light, and it makes the eye shine in your beam.
From the book
Page from A Million Whys Book 4
More fun facts
- Light enters the eye through the pupil, the dark opening in the middle.
- The pupil controls how much light gets in. Both pupils shrink together in bright light.
- At the back of the eye is the retina, a lining full of light-sensitive cells.
- Many night animals have a shiny layer behind the retina, called the tapetum, that reflects light back through the eye.
- That reflecting layer gives the eye a second chance to catch dim light.
- In people, a camera flash can bounce off a blood-rich layer at the back of the eye. That is what causes red eyes in photos.
Sources: Exploratorium, Scientific American, National Geographic
Questions kids ask
Why do a cat's eyes glow in a flashlight beam?
Cats have a mirror-like layer at the back of the eye. It bounces the flashlight's light back out, so the eyes seem to shine.