They can’t. No animal possesses the ability to give light. Stick a
cat in a dark cave and it will not be able to tell the difference between a stalactite and
a stalagmite. Cats are not more able to see in total darkness than humans.
What cats are able to do is to reflect very faint light rays.
When they appear to glow in the dark, cats’ eyes are reflecting what little natural
or artificial light is available in a seemingly dark environment.
The structure that allows cats to reflect light is called the tapetum
lacidum, iridescent layer of cells around the optic nerve. The tapetum ludidum,
is part of the membrane between the cat’s retina and the outer covering of the
pupils. When light is cast upon the tapetum lucidum, it is reflected back as if the
cat’s eyes were mirrors. All cats, including jungle varieties like lions, jaguars,
and tigers, have the capability of reflecting light rays even through they cannot see in
complete darkness.
Cats are fundamentally nocturnal animals. Even though they cannot see
in total darkness, cat’s physiology is designed for them to see much better at night
than their bumbling owners. Cat’s eyes are positioned more forward on their heads
than ours, allowing them a wide field of vision, especially since each eye is capable of
overlapping the others’ sight. With this binocular vision, cats have two chances to
spot a scampering mouse. Cats’ pupils are very sensitive to ultraviolet light,
enabling them to see things humans cannot. The visual purple ion the epithelial rods of
their retina allows cats to catch ultraviolet rays.
Less well known is the fact that by comparison to humans, cats are
veritable Mr. Magoos during the day. Their slit pupils, which make them look so ominous in
Stephen King movies, protect their retinas from the sun. The slits are composed of two
hoods that function as curtains, which can be drawn to let in the sun or pulled together
to clock the sun out. When pulled together, as they often are during the day, a cat’s
vision is extremely narrow.
So cats’ vision is highly overrated. They can’t see well in bright sun, not
at all in complete darkness. They can out see humans only in moderate or dark light --
like in a house, where they spend all of their time.
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