In many of the, now popular, Bigfoot related television shows and documentaries you will hear reference to a phenomena called "Eyeshine." What they are referring to is the belief that Bigfoot’s eyes can glow, usually with a red light. Very little is known about the subject as it pertains to Bigfoot but eyeshine has become synonymous with having a Bigfoot sighting. Youtube is filled with submissions of alleged Bigfoot sightings but are only video of two small lights in the darkness and nothing more. Cryptozoologists all over the nation claim they have seen Bigfoot because they have seen eyeshine in the dark. But here is the million-dollar question; did they see Bigfoot because they saw eyeshine, or did they see eyeshine because they saw Bigfoot? In most of the reports I have read about the owner of the eyeshine could not be identified because it was too dark. The two things that lead people to believe the eyeshine belongs to a Bigfoot is the height at which it occurs and the color of the eyeshine. In almost all the reports I have read about the eyeshine is said to be an average of 8 to 10 feet off the ground and red in color. There are many animals in the woods that display eyeshine but none are 8 to 10 feet in height that I know of.
Before we draw any conclusions we should examine eyeshine closer. Like I said before we know almost nothing at all about eyeshine as it relates to Bigfoot but we do know a little about how it relates to animals and humans. Eyeshine in animals is reflected light that causes animals eyes to appear to glow at night. Now this is reflected light only and is not light produced by the animal, like in cuttlefish, so the animal has no control over it. Animals cannot turn eyeshine off and on at will. What causes the eyeshine is a reflective membrane behind the retina of the eye called the "tapetum lucidum".
Pronounced "ta-pee-tum lu-si-dum", the membrane reflects light back through the eye to its source, just like a bicycle reflector. This allows the rods of the eye to receive a double dose of light, both coming into the eye and leaving the eye. The extra light to the rods allows the animal to see at night. Depending on the shape and position of the tapetum lucidum the light can be reflected in any number of ways allowing different degrees of night vision. In oxen the shape and position of the tapetum lucidum gives the animal about 1 foot of night vision, which allows the animal to identify plants and graze at night. In cats the tapetum lucidum is positioned in a way that reflects light directly back out of the pupil which allows the animal to hunt at night with excellent long-range night vision. While tapetums are not exclusive to nocturnal animals they are rare in diurnal animals. The eyes of nocturnal animals have adapted to low light and not only have tapetum lucidum but also tend to contain more rods than cones. Cones allow the eye to see color and rods aid in low light vision. Diurnal animals eyes contain more cones leaning toward being able to see color over having night vision. Basically if an animal can see color then it does not have tapetum lucidum. Humans and large apes, or dry-nosed primates, are diurnal, can see color, and do not have tapetum lucidum. This seems to be the only pattern currently known to tapetum lucidum. Human eyes have a dark layer where the tapetum lucidum would be and it absorbs light rather than reflects it. In order for tapetum lucidum to create eyeshine they must have light. So animals with tapetum lucidum can only see in low light conditions not in zero light conditions. Zero light conditions, such as in the depths of a cave, render the animal just as blind as you or I would be without light. As a matter of fact animals that live in these zero light conditions are usually blind. Most do not have eyes at all. The light from the moon or stars at night is enough to allow for night vision in nocturnal animals but any light source will work. Campfire light, your porch light, a flashlight, headlights, or any other light can create eyeshine and aid in night vision in animals equipped with tapetum lucidum. It is the source of the light, the angle at which it enters the eye, and the angle at which the resulting eyeshine is seen that dictates the color of the eyeshine. Eyeshine can be any color from white, blue, red, green, yellow, and orange. No one animal gives one exclusive color of eyeshine all the time. All creatures with tapetum lucidum have eyeshine and some form of enhanced low light vision.
These are the facts and cannot be changed. So what do we do with these facts? We must take them and apply logic to our situation. We simply have nothing else to lean on. Does Bigfoot have eyeshine? In order to answer that we need to have the answers to several questions. Is Bigfoot a dry-nosed primate, like Gigantopithecus? Is Bigfoot related to humans? Is Bigfoot diurnal? Can Bigfoot see in color? Logic would dictate that a "yes" answer to ANY of those questions would mean that odds are greatly against Bigfoot having eyeshine. I know what you are thinking; Bigfoot is an undiscovered species that we know nothing about. This is true. Without a specimen to examine we simply do not know the truth, but that doesn’t mean we should allow that fact to be used as an excuse to justify any theory people can make up. We are the only ones researching Bigfoot and we have a responsibility to the public to report the truth and if the truth is that we do not know then that is exactly what we must report. Until we have a Bigfoot to study then applying logic to the facts and drawing an intelligent conclusion is the only recourse we have.
Let's address eyeshine in humans for a minute. While human eyes do not have tapetum lucidum they do not produce eyeshine as eyeshine is defined. However all eyes have a smooth shiny surface and reflect a degree of light just like any shiny surface or glass does. But this light is usually not enough to be seen by the naked eye or usually only shows a glare on the surface of the eye. But cameras are able to see this because of the speed of their shutters. Cameras are also fast enough to capture what is known as red-eye in color photos of human eyes. While many consider this to be related to eyeshine it is not the same thing. What causes red-eye in color photos has more to do with the proximity of the flash to the lens and the ambient light than to the function of the eye. Almost all compact flash equipped cameras have the flash close to the lens, unlike professional camera setups where the flash is separate from the camera and sets high above or off to the side of the lens. Having the flash away from the lens is to avoid the red-eye effect in low light conditions. In low light the pupil of the eye is open wider to allow more light in. The lower the light conditions the wider open the pupil is. When a camera flashes in low light conditions the human eye cannot close the pupil fast enough to protect it from the bright light. The flash is so fast that the dark layer of the human eye that normally absorbs light cannot absorb the light from the flash fast enough. Therefore the photo catches the pupil wide open and spilling over with light. It is blood that produces the red color. Having the person in the photo look away from the camera can reduce this problem.
Dealing with infrared light and cameras such as those equipped with the Sony Night Shot feature can have similar effects. I am not talking about thermal imaging cameras that see infrared heat. I am speaking of cameras that use infrared light. In animals with tapetum lucidum the infrared cameras pick up the reflected ambient light from the eyes much easier, causing them to look brighter than they actually are. In humans the eyes can appear to have the same type of eyeshine. But it is not eyeshine at all. What causes it in humans is the same thing that causes the red-eye effect; the eye’s inability to absorb the light. The low light conditions cause the pupils of the eyes, human and animal, to open up. In very low light, like at night in the woods, the pupils will open up completely allowing cameras to see directly into the eye. In animals with tapetum lucidum this allows the camera to see all of the light reflected from the eye, including the IR light. The human eye does not see or need IR light to function and the eye discards it. At the right angle the camera can see this IR light and it appears as if the person’s eyes are glowing with eyeshine. While this is commonly referred to as eyeshine it is not, as true eyeshine requires a tapetum and this phenomena is only possible with infrared light using an infrared camera and cannot be seen by the naked eye. This type of eyeshine is also uncommon, In 5 years of using infrared cameras I have only seen it happen naturally once. The effects of red-eye and IR eyeshine can be purposely reproduced and are sometimes used in art. The effect was purposely used in the filming of Blade Runner to show the difference between humans and androids.