The pupils of a deer are elongated. Think of their proportion as the general shape of a tootsie roll. Because of the position of the eyes on the head and the shape of the pupils, the deer have a constant viewing area of approximately 300 degrees, with the remaining 60 degrees to their rear. See Figure 1.
Now, the interesting part is that because of the elongated pupil, the extended viewing area, and how they process that information, they see everything within that viewing area relatively clearly and all at once. Humans must focus on one thing at a time by moving our eyes quickly from one location to another. By not having to move their eye from one thing to another to focus, they can easily detect the slightest movements. Like all things though, this comes with a price. Due to the elongated pupil to help with what I just described, they cannot see up or down very well. The vision is clear as they hold still and becomes slightly out of focus as it reaches a certain point, either going up or down. Obviously, they can overcome this by moving their heads. However, since they traditionally do not have predators above them, they tend to move their heads more towards the ground to watch where they are stepping (Stealth), for food, and predators. This is why hunters have been so successful in a tree stand and not on the ground.
But… there is another reason that hunters aren't so successful on the ground.
Deer have dichromatic vision, meaning they have two types of color receptors in their eyes. This gives them a limited color perception that's best suited for their crepuscular nature and habitat. I have attached a chart below (Figure 2) to demonstrate the differences between our vision and theirs. If you look, you will see that they can see well into the UV spectrum that we can't. I have attached a chart below (figure 2) to demonstrate the differences between our vision and their vision. If you look, you will see that they can see well into the UV spectrum that we can't.
Here is the problem with that. We have a UV filter, but they do not. So some of the camo we wear is really only designed for people and not animals, including TURKEY, which can see into this spectrum as well. It turns out that certain manufacturers of camo/ hunting clothes have brighteners to make the camo richer in color, which attracts us to buy it because it looks good. These brighteners also exist in almost every laundry detergent. These brighteners and phosphates in the detergents fluoresce in the UV spectrum, which we can't see, but they can. An example is Figure 3.
You may be saying what???? I took some pictures of my camo outside with our UV/IR Camera from work during midday in the shade. Our camera is a full spectrum camera that captures all of the wavelengths. I used a UV 403 nanometer filter, which only allowed that specific wavelength of light to pass. It should be noted that this is on the low end of the area where the deer can see UV, so the colors aren't going to be as vibrant. It doesn't show the blue glow as well, but that would be higher up on the spectrum. This does give a close idea of the real world of what a deer would see when it is looking at the camo. There is something of interest in the photos. The shirt hanging in the tree lost its pattern completely and is glowing slightly blue (Figure 4 No. 1). No doubt it would be much brighter if the filter was not only allowing light in the 403-nanometer wavelength. There is a balaclava hanging directly above it that lost its pattern as well but stayed true to the colors in its surroundings (Figure 4 No. 2). There is a shirt and pair of pants in the bush to the right. You see what happens there (Figure 4 No. 3). The Turkey vest is at the base of the tree (Figure 4 No. 4). I Guess when I wear that, I will be up against the pine trees as they are about the same value in the picture as the camo.
The easiest way to see the glow is to use a simple UV/ black light like the kind you look for pet urine with. Here’s an example from my own closet. See Figure 6.
As you can see in figure 6 at the bottom, there is a distinct blue glow on the left and a purple on the right. The bright blue are the brighteners that the deer can see. The purple is what you want. It should be noted that the clothes with the blue glow came from the manufacturer like this and was not a result in washing them in a detergent with brighteners.
So it turns out that there are ways to help mitigate the blue glow. There are UV Killers for sale on Amazon.com and other websites.
I have now tried the UV killers and they do work but must be re-applied occasionally as they become less effective with every wash. Even so, it was not 100% effective.
Also something to consider. If wearing the camo that looks super dark behind the yellow bush and there is movement, or the shape of a person, this may also be beneficial way for us to find people as well. Looking for deer, turkey, or humans, this knowledge can be applied in different ways. It should also be noted that the military is very aware of the UV glow. The military only sells laundry detergent without the color brighteners on their bases. Some laundry detergent companies make a version of the popular brands without the brighteners just for the military.
Just something to consider if you're trying to take the stealth approach while looking for Bigfoot, since we have absolutely no idea how a Bigfoot eye works.
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