Night Vision Optics – Human Versus Animal
Even in the dark, most of us can still see. Well, we can see up to a point. Animals, on the other hand, are able to see a lot more detail in low-light or no-light situations than us and the following explains some factors, both biological and environmental, that make this possible.
Augmented Human Vision We have two ranges that we incorporate to intensify our night vision they are known as the spectral range and infrared range. When we use our spectral range it allows us to take advantage of what is normally invisible to the naked eye. We can see into the infrared and ultraviolet spectrum's with the aid of such products as night vision goggles and binoculars. Special infrared optics in digital camera's also allow us to see within the infrared spectrum and can be used in thermal imaging as well.
Biological Human Vision As humans we have three types of vision that we naturally use in order to be able to see within any lighting situation, they are known as photopic, mesopic and scotopic. We see over a range of several million to one and with the photopic vision we see the highest light levels and this is what we use in the daytime. Scotopic works in extremely low light situations while our mesopic vision is what we use in low-light when no detail can be seen. When human eyesight goes from bright to dark, or dark to light it can take up to forty-five minutes for the eye's to adjust properly, but with animals it happens immediately.
Tapetum Lucidum A number of vertebrate animals rely on a layer of tissue called the tapetum lucidum located behind or within their retinas. There are four types of tapetum lucidum found in the variety of animals on the planet. This masterpiece of nature allows the light to be refracted back into the retina, allowing animals to have augmented vision which enables them to see in the dark. This happens instantly for them. The eyeshine you see in animals like cats, dogs, deer when light hits their eyes in the dark is a result of the tapetum lucidum. The eyeshine can occur in different colors like red, green or blue, depending on the animal.
Biological Animal Vision These are a few examples of how different animals can see in the dark.
Pit Vipers, and many other snakes, find their prey at night by smell and tasting the air and the use of deep pits on the side of their head that help them detect heat as a form of thermal vision.
Fruit Bats have a folded retina that they use in conjunction with sonar allowing them to navigate and find food in the dark.
Owls have the ability to see small animals at the distance of a football field away. They have special lenses that can magnify information in the same way a telescope does.
Rays and sharks have flat refractive crystals of guanine that activate in murky waters to allow better sight.
So as far as the naked eye is concerned it's pretty obvious that many if not all animals have a definite edge over us humans when it comes to seeing in the dark. But as luck would have it us humans have been able to develop night vision technology to the point where we can see very clearly in almost total darkness. But if you think your eye's can now compete with those of an animal I'm afraid you are sadly mistaken.
By Craig Mooney
Night vision technology has advanced so much in the past few years that it is being used in everyday life. Night goggles are frequently used for surveillance by security companies and outdoors men have incorporated the technology into their hunting scopes which enables them to hunt at night when most wild life are active.
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