Answered: Why the eyes of some animals glow at night

According to the Encyclopædia Britannica, the tapetum lucidum is a reflective layer of tissue found in the eyes of many vertebrates, primarily nocturnal animals like cats, dogs, deer, raccoons, and alligators.

It reflects visible light through the retina, increasing the light available to the photoreceptors. Basically, when light hits their eyes—say, from your torch or a car’s headlights—it bounces off that shiny layer and comes back out, making it look like their eyes are glowing.

This adaptation significantly enhances an animal’s ability to see in low-light conditions. Humans don’t have this mirror layer in their eyes, so our eyes don’t glow.

Why do they need it?

Animals that are active at night or in low light (nocturnal and crepuscular animals) need to be able to see when it’s dark. The tapetum gives their eyes a “second chance” to catch light. This makes it easier for them to hunt, avoid danger, or move around safely in the dark.

According to the Encyclopædia Britannica, the tapetum lucidum is a reflective layer of tissue found in the eyes of many vertebrates, especially nocturnal animals like cats, dogs, deer, raccoons, and alligators (Source: Wikimedia Commons)

Depending on the animal, the glow can show up in different colours:

• Cats and dogs: usually greenish-yellow or blue
• Deer and raccoons: often bright white or golden
• Alligators: reddish or orange—especially spooky in the dark!

According to veterinary sources cited by National Geographic and Scientific American, the tapetum lucidum increases visual sensitivity by up to 50%.

Interestingly, not all animals with excellent night vision have eyeshine. Even though owls are great at seeing in the dark, they actually don’t have this glowing layer. Instead, they have big eyes with lots of special light-catching cells.

Is it the same as humans getting red eyes in pictures?

You might’ve seen red eyes in photos of people taken with a flash. That’s not the same thing. That red comes from light bouncing off the blood behind our eyes. It’s not nearly as cool, but it’s still a similar idea!

That glow, often called “eyeshine,” isn’t just a spooky nighttime effect. It’s super helpful in the wild. It helps animals survive in the dark, and for us humans, it helps in wildlife photography, tracking animals at night, and even understanding pet behaviour better.