DO HUMANS AND PRIMATES HAVE REFLECTED GLOW OR SHINE AT NIGHT ?

Yes, but not like cats do, when you photograph a cat’s eyes at night you see a strong reflection because the eyes are shaped to gather more light in the dark and reflect it better than in human eyes. This is referred to as eye shine.

Human eyes do reflect back the light the problem is called the “red eye effect.” Humans lack the highly reflective tapetum lucidum membrane in the eye of cats and other hunting animals, though so they don’t reflect as much light back.

“The red-eye effect in photography is the common appearance of red pupils in color photographs of eyes. It occurs when using a photographic flash very close to the camera lens (as with most compact cameras), in ambient low light. Red-eye effect appears in the eyes of humans and animals that have no tapetum lucidum, hence no eyeshine, and rarely in animals that have a tapetum lucidum. The red-eye effect is a photographic effect, not seen in nature.

Because the light of the flash occurs too fast for the pupil to close, much of the very bright light from the flash passes into the eye through the pupil, reflects off the fundus at the back of the eyeball (see diagram in Eye), and out through the pupil. The camera records this reflected light.”

“The tapetum lucidum (Latin: “bright tapestry”, plural tapeta lucida) is a layer of tissue in the eye of many vertebrate animals, that lies immediately behind or sometimes within the retina. It reflects visible light back through the retina, increasing the light available to the photoreceptors. This improves vision in low-light conditions, but can cause the perceived image to be blurry from the interference of the reflected light. The tapetum lucidum contributes to the superior night vision of some animals. Many of these animals are nocturnal, especially carnivores that hunt their prey at night, while others are deep sea animals. Although some primates have a tapetum lucidum, humans do not.

Eyeshine is a visible effect of the tapetum lucidum. When a light is shone into the eye of an animal having a tapetum lucidum, the pupil appears to glow. Eyeshine can be seen in many animals, in nature and in flash photographs. In low light, a hand-held flashlight is sufficient to produce eyeshine that is highly visible to humans (despite our inferior night vision); this technique, spotlighting, is used by naturalists and hunters to search for animals at night. Eyeshine occurs in a wide variety of colors including white, blue, green, yellow, pink and red. However, because eyeshine is a form of iridescence, the color varies slightly with the angle at which it is seen and the color of the source light.

White eyeshine occurs in many fish, especially walleye; blue eyeshine occurs in many mammals such as horses; yellow eyeshine occurs in mammals such as cats, dogs, and raccoons; and red eyeshine occurs in rodents, opossums and birds.

The human eye has no tapetum lucidum, hence no eyeshine. However, in humans and animals two effects can occur that may resemble eyeshine: leukocoria (white shine, indicative of abnormalities including cataracts, cancers, and other problems) and red-eye effect (red shine, apparent only in flash photography).”

Daniel Benoit ( founder & ceo )

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