Science indicates deer hunters should be concerned about the blue “glow.”
The decoy looked as real as a decoy can get. It was covered in a thin cloth printed with all the details of a real whitetail, right down to a gleam in the eyes. So what spooked the buck? It wasn’t me. I stood motionless, covered head to boots in full camouflage as the buck eased into the field 100 yards away.
I’ve been closer to mature deer while wearing a blaze orange vest and hat. He had no idea I was there, and he never looked at me. Instead, he immediately focused on the fake doe in the cornfield 20 yards in front of my stand. A second later, he turned and bolted as if I’d fired a slug at the ground in front of him.
I was on a bowhunt sponsored by a company that manufactured and sold decoys. Later that morning, my host made a quick call back to headquarters. His suspicion was confirmed. The decoy had not been factory treated with an ultraviolet killer.
It was a valuable lesson I still consider when I buy any new product made from cloth: A buck that locks on to you might not be seeing you. He might be seeing a radiating shade of blue from your clothing.
Millions of hunters have killed millions of deer without any thought to the impact their clothing has on their success. If you sit still long enough, a buck will eventually wander past. But, as I learned that December day in Illinois, some fabrics stand out like a lighthouse on a pitch black night.
Why? They are treated with a color enhancer that basically turns ultraviolet light into a shade of blue. We can’t see it, but whitetails can.
“I hear from hunters all the time who experience similar things,” says ATSKO vice-president Dan Gutting, whose company makes products that kill UV light. “They were sitting perfectly still when a deer took one look at them and bolted.
“Clothing is typically treated with a color brightener to make the colors more vivid,” he continued. “And most laundry detergents have color brighteners to keep colors vibrant longer. That color brightener enhances all colors, including ultraviolet – and that’s what deer see.”
Ultraviolet light is at the extreme edge of the light spectrum. Remember ROY-G-BIV from grade school science class? It stands for the visible bands of color in human vision: red, orange, yellow, green, blue, indigo and violet. Ultraviolet falls outside our vision, which is most acute between approximately 500 and 650 nanometers (the unit used to measure wavelength of electromagnetic radiation). UV light measures around 400 nanometers, which is why we don’t see it.
Whitetail eyes are most sensitive between 430 and 540 nanometers, says University of Georgia research scientist Dr. Bradley Cohen. That’s in the blue and yellow spectrums, but it also includes ultraviolet, which falls outside the range of human vision.
Because blues are more visible to whitetails in low light conditions, they can see the UV light emitting from clothing. In fact, UV light is most visible in shadows and under heavy cloud cover, and in mornings and evenings when deer tend to be most active.
HOW DEER SEE
Cohen says whitetails don’t see the glow hunters often think of when they talk about UV light.
“If you are standing in a dark background, you are just bluer to a deer,” he notes. “We don’t see the blue, but deer see it better than we do.”
Hunters tend to generalize their idea of a whitetail’s senses. We assume they are color-blind because they can stroll past a blaze-orange-clad hunter seated at the base of a tree. It’s true that whitetails are color-blind, but only to a point. Their eyes are dichromatic. They have two cones (the cells responsible for interpreting light and color), while humans have three. Deer lack the cone sensitive to reds and oranges, which are around 600 to 700 nanometers.
Cohen tested the perceptual sensitivity of whitetail vision for his master’s thesis at the University of Georgia. Previous studies confirmed deer see colors, but Cohen’s examined their perception of different light wavelengths, or how they react to them.
Titled “Behavioral Measure of the Light-Adapted Visual Sensitivity of White-Tailed Deer,” his study showed their perception of reds and oranges is different from ours.
“One of the basic rules of psychology is that just because something is present does not mean you perceive it,” explains Cohen. “We measured the perceptual sensitivity of deer vision.”
He trained seven pen-raised whitetail does to get a food reward when they saw various wavelengths of light. He tested various wavelengths in the blue range of the color spectrum and in the red range. He says the animals had to actually perceive the light to get food. He found whitetails see blues, greens and yellows, but they can’t perceive reds and oranges, at least not in the same way we perceive them.
Cohen said deer likely see reds as yellows or even closer to shades of gray. That’s why they walk past a hunter wearing blaze orange without seeing him.
“They can see some blues 20 times better than humans,” he adds. “It was unbelievably different.”
Those blues include ultraviolets that humans can’t see. We have a UV screen, of sorts, built into our eyes. It blocks much of the UV light emitted by the sun, preventing us from seeing colors in the UV spectrum. Whitetails don’t have that UV screen.
Our eyes are different from a whitetail’s in other ways, too.
“Ours are made to identify objects,” Cohen said. “Deer eyes are made to detect movement.”
That’s likely a result of the evolutionary process that helps deer survive predators. They need to see the sudden lunge of a coyote or wolf more than they need to see the predator itself. Cohen says the eyes of other prey species are likely similar to those of a deer’s for the same reason.
Their pupils can be opened wider than ours, which is one reason they can see better at night. No matter what time of day it is, we can beat their eyes fairly easily if we sit still as they walk into view. However, we can’t outwit a buck under some conditions if our clothes are reflecting UV light.
TREAT IT. OR JUST WAIT
Cohen says a great many hunting clothes are treated with brighteners. He examined a number of unwashed clothing items under a spectrophotometer and measured the percentage of light being reflected.
“There were some that really stood out,” he said.
Why wouldn’t they? Just as fishing lures are designed to catch fishermen first, hunting clothes are marketed to hunters. The brighter and more vivid the patterns and colors, the more likely they are to catch your eye — and your credit card. Gutting said he’s seen camo outerwear with a patchwork of material that glows.
“Sometimes the pockets or the arms will emit UV light while the torso doesn’t,” he said. “It depends on the cloth that was used to make the outfit.”
A few manufacturers label their outerwear as UV-free. Unless it’s labeled, there is no way to tell without some help. The only way to determine if your outerwear is reflecting UV light is to hold it under a black light — unless you want to test it on live deer while you’re hunting.
Hang your hunting clothes in a small room, turn off the lights and turn on a black light. If your clothes contain UV brighteners, you’ll know right away by the blue glow. Be warned, though. Not all black lights are the same. Some are nothing more than incandescent bulbs with a clear purple coating on them. They don’t work, says Gutting. Others don’t emit enough UV light to reflect off clothing.
“You need a fluorescent bulb that is a true black light,” Gutting adds.
If your clothing doesn’t look bright blue, you’re good. That means it isn’t reflecting UV light.
Cohen says most UV brighteners eventually wear off. Older camo that has not been washed in a detergent with a UV brightener likely won’t reflect UV light.
If your clothing does glow, spray it with a UV killer and always wash it in a detergent that does not have brighteners. Gutting explained UV killers absorb the energy emitted by UV light, changing the blue light into green. It’s a little more complicated than that, he admits, but it does effectively end the risk of a deer seeing the UV light reflecting from your outerwear.
Cohen, however, says the simple act of washing your new clothing once in water without a detergent will usually reduce the UV reflection, unless the brightener is in the dye used to make the camo pattern. If that’s the case, you might need to use a UV killer on occasion. Don’t assume washing your clothes or spraying them with a UV killer makes you invisible, though. You still have to play the wind; you have to sit still and you have to make your shot count.
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This article was published in the August 2014 edition of Buckmasters Whitetail Magazine. Subscribe today to have Buckmasters delivered to your home.