By Arden Moore, a certified cat and dog behaviorist with the International Association of Animal Behavior Consultants. Arden is an author, radio host, and writer for Pets Best, a cat insurance and dog insurance agency.

I was asked the following question by a cat owner, “When I walk around my house at night in dimly lit rooms, sometimes I get spooked a bit when I see my cat. Precious is a sweet Siamese cat, but at night, her eyes seem to glow red in the dark, giving off a devilish look…What causes her eyes to glow red at night?”

Good question. Your cat’s large, round eyes are designed to operate far better in low light conditions and the dark than our eyes. As hunters who are active at dawn and dusk – the best times for them to stalk prey – cats can actually see as well in pitch black as we can see in full moonlight. Here are two reasons cats’ eyes glow in the dark.

1. Take a look at her eyes some evening under a bright lamp. Notice that the pupils are elliptical in shape, compared to our circular ones. In the lamplight, the pupils are narrow slits because they are protecting the sensitive retinas from damage. Now turn the lamp off and notice that her pupils dilate to accommodate the lower lighting. In a very dim light, the pupils will fill her eyes, making them look almost completely black.

2. As for that red glow, it is caused by light reflected from a layer of tissue called the “tapetum lucidum,” which lines the back of the eyeball behind the retina. It acts like a mirror, reflecting light that was not absorbed the first time it passed through the retina back through the eyes onto the light sensor cells in the retina. The result is an eerie glow as your cat’s eyes catch a beam of light in a dark room. This term, tapetum lucidum, is a Latin phrase that means “bright carpet.”

Interestingly, some feline eyes glow green rather than red depends on the color of the cat’s eyes. Blue eyes, which Siamese cats have, glow red, while golden and green eyes cast green glows at night.

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