How Game Animals See & Smell

How Game Animals See & Smell
by Kurt von Besser ATSKO/SNO-SEAL Inc.

Printed in U.S.A. - 1993

Front covers, courtesy of Jay Neitz, Ph.D. Vision Scientist Medical College of Wisconsin



These graphs illustrate the difference between the Daylight (color) vision of the Human and the Whitetail deer. Each trace reveals the profile of sensitivity of a single class of receptor. Notice that the deer has only blue peaking and green peaking receptors while the human has a third receptor that is normally referred to as "red" because it gives us the ability to see red light. This third cone makes us far more sensitive to the longer wavelengths (such as blaze orange at 605 nanometers). Notice also that the sensitivity of our blue receptor and the short side of our green receptor are lower than that of the deer. This is the result of our UV Filter that is absent in the deer. It makes us unable to see UV and far less sensitive to all wavelengths from 500 nanometers down. The color bars illustrate the full range of color and brightness that each would see if deer and human both observed the same equal brightness rainbow.



Scotopic or rod vision is the black/white/gray capability in low light conditions at the peak hunting hours when these animals are most active. While deer are clearly superior in low light at all wavelengths, the advantage is greatest at wavelengths where the deer's sensitivity continues after human vision has ceased (Blocked by the UV Filter). This graph illustrates the extended capability of game animals and birds to see beyond our visible range. Note that at 400 nanometers (where human vision is fully blocked by our UV filter) the game animals have greater sensitivity than we do at the peak of our human sensitivity. For ease of illustration, a logarithmic scale is used to compress the huge advantage in rod sensitivity of the deer.

My fellow outdoorsmen, we've come a long way since I saw the light caused by laundry brighteners activated as I walked under a UV bug zapper in Montana. Much has been written in the popular press and while almost all camo is now made free of UV brighteners, a few doubters (most of whom also question the sphericity of the earth) are still waiting to find a talking deer. A couple of recent studies provide new insight to deer vision and to the spectral profile of blaze orange in variations of ambient light.

North American white-tailed deer have been tested! The research was conducted from August 24 to 29, 1993, at the University of Georgia, D. B. Warnell School of Forest Resources, in Athens, Georgia. Present were Dr. R. Larry Marchinton and Dr. Karl V. Miller of the University of Georgia with a staff of graduate students headed by Brian Murphy as research coordinator. The electroretinograph was administered by Dr. Gerald Jacobs and his assistant Jess Deegan of the University of California at Santa Barbara, assisting was Dr. Jay Neitz of the Medical College of Wisconsin. The Electroretinograph equipment, provided by Dr. Jacob's lab at the University of California, is the culmination of 12 years of refinements. Computer controlled light presentation and signal processing now enable scientists to accurately define the range of vision in animals.

The details of this work were publicized for the first time at the annual meeting of the Southeast Deer Study Group. This meeting was hosted by the Mississippi Department of Wildlife, Fisheries, and Parks and was held February 21 through 24, 1993, at the Holiday Inn North in Jackson, Mississippi. This study on the vision of the white-tail deer was presented by Dr. Karl V. Miller of the University of Georgia.

Following is the abstract of what was presented.


Brian P. Murphy, Karl V. Miller, and R. Larry Marchinton, University of Georgia; Jess Deegan, University of California; Jay Neitz, Medical College of Wisconsin; Gerald H. Jacobs, University of California.

All aspects of vision depend ultimately on the absorption of light by photopigments. The retinas of white-tailed deer (Odocoileus virginianus), like those of other ungulates, contain a mixture of rod and cone photorecep-tors. We have used a noninvasive electrophysiological technique to measure the spectral absorption properties of the photopigments contained in these receptors. In this procedure, electroretinogram (ERG) flicker photometry, light-evoked potentials were sensed by a contact-lens electrode positioned on the eye of an anesthetized deer. The eye was stimulated with a rapidly-pulsed, monochromatic light; variations in pulse rate, stimulus wavelength and adaptation state of the eye allowed preferential access to signals from different classes of photoreceptor. Recordings were obtained from nine white-tailed deer. Three classes of photopigment were detected. One of these is the photopigment contained in rods; it has a peak sensitivity of about 496 nm, a value greatly similar to that found for rod photopigments of other mammals. These measurements also reveal the presence of two classes of cone. One contains a photopigment maximally sensitive in the middle wavelengths (peak value of c. 537 nm); The other cone class has a sensitivity peak in the short wavelengths, at about 455 nm. In light of what is known about the relationships between photopigments and vision in other species, these results suggest two likely characteristics of cone-based (i.e., daylight) vision in deer: (1) deer should be relatively less sensitive to long-wavelength lights than many other mammals (e.g., humans), and (2) white-tailed deer would be expected to have dichromatic color vision.

In addition to this study which used the ERG to detail the spectral sensitivity of the deer, there have been recent spectro radiometric studies of ambient light and blaze orange with and without U-V-KILLER treatment. Following is an interpretation of the results of both of these studies by Dr. Jay Neitz.


Vision is initiated when light is absorbed by photoreceptors of the retina, the light absorbing tissue that covers the back of the eye. The limits of vision depend on several factors which include:

(1) The optical properties of the eye, i.e., the size of the eye, the size of the pupil, the refractive power of the eye's optical elements.

(2) The properties of light absorbing filters through which light must pass before reaching the photoreceptors. In humans these include filters in the lens and in the central region of the retina that absorb strongly in the short wavelengths, blue, violet and ultraviolet.

(3) The light absorbing properties of the photoreceptors themselves, the number of different classes of photoreceptors and their distribution in the retina.

(4) The reflectivity of tissues that lie behind the photoreceptors. For example many animals that are active in dim light have a reflective layer at the back of the eye that enhances sensitivity.

Some of these properties have been recently investigated for the eyes of white-tailed deer. A non-invasive procedure (harmless to the deer) was used on anesthetized deer to measure the sensitivity of the deer's eyes to wavelengths of light across the spectrum.

Deer like all other mammals have two types of photoreceptor, rods and cones. The rods are responsible for vision in dim light and the cones are responsible for vision in daylight. The light absorbing properties of the rods in deer were found to be similar to those found in other mammals, including humans. Two classes of cone photoreceptor were detected in the deer. One most sensitive to short-wavelength light (blue-violet); the other most sensitive to middle-wavelength light (green-yellow).

The lens of the human eye contains a yellow pigment that absorbs ultraviolet light almost completely; it absorbs strongly in the violet and into the blue spectral regions. In contrast, the transmission of short wavelength light is very high for the lens of many mammals that are active at dusk, dawn and at night. The recent experiments indicate that this is true for the deer. The relative sensitivity of deer eyes to short wavelengths (blue and violet) is high compared to that of humans, as expected because deer lack yellow pigment in their lens.

In humans, the very central region of the retina (the fovea) is specialized for high acuity vision. Among mammals, this specialization is found only in humans and other primates. Also unique to primates is an additional yellow pigment, the macular pigment, that covers and thus screens the central region of the retina. Humans use the central region of the retina whenever we look directly at an object; it is this region that we depend on most heavily for vision. Thus, when comparing the daylight vision of deer to that of humans it makes sense to consider human foveal vision. The recent experiments suggest important differences between the daylight vision of deer compared to that of humans:

(1) Humans have three classes of cone photoreceptors which are the basis of trichromatic (literally three-color) vision. In humans this three-receptor system confers excellent color vision. Humans can distinguish small differences in wavelength across the spectrum. In contrast, only two classes of cone photoreceptors were detected in deer. Deer can have no better than dichromatic (two-color) vision. Thus, the color vision capacities of deer are, at best, limited compared to humans. The two classes of cones in deer allow for the ability to see color differences between short and long-wave lights, e.g., blue and yellow, however, they lack the photoreceptor basis for seeing differences in the color of objects that reflect middle-to-long wavelength light, e.g., yellow-green, green, yellow, orange, and red.

(2) Since humans have yellow pigments that screen out short-wavelength light, the relative sensitivity of deer to short wavelength light is much higher than the sensitivity of humans. This same difference would apply to low light conditions under which only rod photoreceptors operate.

(3) The three classes of cone photoreceptors in humans are each sensitive to a different region of the visible spectrum. Togetherthese confer sensitivity to a wide band of wavelengths. The three classes of human cone photoreceptors can be termed red, green and blue cones. One of the two cone photoreceptors detected in deer is similar to the human blue cones; the other is similar to human green cones. Thus, compared to humans, deer effectively lack red cone photoreceptors. This suggests that deer should be relatively less sensitive to long-wavelength light (orange and especially red) than humans.

Human sensitivity is highest in the green-yellow region of the spectrum and, for equal intensities, these wavelengths are perceived as brightest. Humans are relatively insensitive throughout the short-wavelengths (blue and violet). Sensitivity also drops off rapidly in the very long wavelengths, e.g., we are relatively insensitive to deep reds. Humans can distinguish four basic colors; blue, green, yellow and red. We also distinguish dozens of intermediate colors, e.g., violet, blue-green, yellow-green, orange etc. Humans can make subtle color discriminations across the visible spectrum.

The region of highest sensitivity for the deer is at a shorter wavelength than that of humans. The relative sensitivity of deer to short-wavelength light is dramatically higher than human sensitivity to those wavelengths. For equal intensities, deer are expected to see short- and middle-wavelengths as brightest. Because of the absence of red cones, the drop off in sensitivity at the long-wavelength end of the spectrum occurs at shorter wavelengths for deer. They are less sensitive in the spectral region that appears orange to humans and are virtually insensitive to deep reds. With only two classes of cone photoreceptors, deer can distinguish no more than two basic colors, one for the short wavelength end of the spectrum and another for the middle-to-long wavelength end of the spectrum. Animals with dichromatic color vision do not see an intermediate color in the spectral region between the two colors. That is, they do not see a color that appears bluish-yellow. Instead they see the intermediate spectral region as colorless (gray).

The issue of how deer see blaze orange is of considerable interest to hunters and those interested in hunter safety. Recent results lend insight into how deer may perceive blaze orange. Blaze orange is highly visible to humans because, for us, it is both intensely bright and intensely colored. The worst news for hunters would be if blaze orange was seen by deer as intensely colored and intensely bright as it is for humans. At the other extreme, perhaps the best news would be if blaze orange was not seen at all by the deer. Given what is known about deer vision neither of those extremes is likely to be true. The recommended specification of blaze orange requires a dominant wavelength between 595 and 605 nanometers. Deer are expected to see this band of wavelength. However, the deer's relative sensitivity to 605 nanometers is less than half the relative human sensitivity. Although 605 nanometers is expected to be seen by deer as colored, that color would not be different from long-wavelength lights (the ones we see as red, yellow and yellowish-green).

Wavelengths that deer are likely to be able to distinguish from 605 nanometers are the ones we see as violet, blue, blue-green, and pure green. A garment that emitted only an intense band of light at 605 nanometers would be less colored and less bright to deer than it is to humans. However, it is important to understand that such a garment would be far different from an ideal camouflage. It would still stand out as colored and/or bright against dark backgrounds, against bluish-greens, pure greens, browns, tans, and grays.

Finally, the issue of how deer see short-wavelength light has received considerable attention. Recent results also lend insight into this issue. The difference between daylight human foveal vision and daylight deer vision is expected to be even more dramatic for short-wavelength light than it is for long-wavelength light. Humans are very insensitive to wavelengths below 450 nanometers. For example, relative to other wavelengths, deer are about eight times more sensitive than humans to lights of wavelengths near 430-440 nm (such as those emitted by UV brighteners). Garments can reflect (or emit) considerable light in this spectral band. Because of the deer's high relative sensitivity to short wavelength light, the presence of blue, violet and U V components would make a garment stand out as both bright and colored against natural backgrounds. Those same components could be barely noticeable to humans." Dr. Jay Neitz

This information about color vision is also summarized by the graphs on the outside front cover.

We shall now examine the significance of these findings to the Hunter.

Much has been written lately about how UV brighteners effect a deer's perception of camouflage , blaze orange, and other garments. In order to apply what has been learned about the visual systems of the deer we must define how brighteners effect the garment being seen. This is further complicated by the spectral composition of the ambient light in which the garment is viewed.

We can simplify the effects of variations in ambient light by simply assuming that, for the sake of a discussion about the effect of UV brighteners, we are talking about a time and place where UV is a high percentage of available light. In direct sun at high noon the longer wavelengths overwhelm our visual system completely and we see no effect from UV brighteners. As we move to dusk, dawn, deep overcast, or shade the absolute amount of UV and short blue light decreases, but the fraction of total light contributed by UV increases greatly. We therefore confine discussion of brighteners to times and places where their effect is significant.

The garment's color and other optical characteristics are also significant. Ignoring most variations again allows us to focus on the effects of brighteners. It will be noted, that for humans (very insensitive to UV and short blue wavelengths) the effects could only be observed (if at all) on white or light colored garments. The deer, however, should see these effects on almost any color. The background is also significant. If a hunter is forced to silhouette against a sky that is rich in UV he may want to match this intensity just as he would try to match the lack of UV from a tree trunk or grass. Now lets consider what a UV brightener is. There are about 200 compounds in a handful of families that absorb light energy in the UV portion of the spectrum. Also called fluorescent whitening agents, brighteners undergo a temporary change (using up energy) and then release the remaining energy at a longer wavelength. The compounds that protect paint or plastic from UV damage and the whitening agents in cloth and laundry detergents generally release the energy they gathered through the UV spectrum in a small band of short blue wavelengths at about 440 nm.

Here we can apply what has been learned about the deer's ability to see short wavelengths. "Deer are much more sensitive than humans to the shorter wavelengths of light." They have been found to have a blue cone with peak sensitivity at 455 nm, just 15 nm from the 440 nm peak of spectral power caused by the brighteners. This is earth shaking news to a 2 legged predator that can't imagine the brightness of light he barely sees. This 440 nm light is seen as bright blue in the dichromatic eye of the deer. It occurs on garments of any color from camo to blaze orange if brighteners are present. In very low light the deer, like a human, switches to rod (black, white, and gray) vision and the 440 nm light caused by the brighteners is seen by the deer as a much brighter gray.

The research also verified that "Deer are much less sensitive to longer wavelengths than humans". This means that if a blaze orange vest had no brightener dyes and was purely 605 nm blaze orange the deer would not see it nearly as well as we do. They lack our red cone completely. Their green cone peaks at 537 nm, almost 70 nm away and pigment sensitivity curves drop steeply on the long side. Dramatic as this difference in sensitivity is, it is only part of the story. Remember the third finding of this study. "White-tailed deer would be expected to have dichromatic color vision". Human dichromats called protanopes also lack the red cone function. A human with one dichromatic eye ( blue/green cones ) and one trichromatic eye ( blue/green/red cones ) can tell us the difference in color perception. They see blue as blue and the rest of the spectrum from green to red as the color yellow, with their dichromatic eye. Therefore, if blaze orange or most green/brown camouflage is without brightener effect, it is all yellow. It will all blend in well in a world of green leaves, yellow grass, and brown trees, because they too are all yellow.

Now consider what effect U V brighteners would have on these garments that appear yellow in a yellow world. Blue flags? Yes, but only on blue, white, light shades of gray, and other colors that have some blue content. Other colors will simply appear brighter and whiter much as intended for humans. In low light the problem is even greater. Many subtle differences in physiology make the deer far more sensitive to dim light -especially shorter wavelengths. They switch to black and white rod vision as humans do but can detect light 1000X below our threshold in the blue and U-V wavelengths. What can be done to help the hunter? How can he safely wear blaze orange and minimize his visibility to deer? Simply be sure that his clothing is as dark as possible in all wavelengths below 440 nm.

The top quality camo manufacturers all take care to ensure that their garments are made without UV brighteners. You can be sure you will not glow if you choose a brand with a hang tag saying they have avoided brighteners and that the item should be washed only in SPORT-WASH to keep it that way. Garments can be checked with a fluorescent UV light source using a bulb labeled "BLB". If your favorite old camo suit has been washed with a detergent containing brighteners simply re-wash it in Sport-Wash and treat it with U-V-Killer. All blaze orange is presently made with brighteners and must be treated with U-V-Killer. It will reduce UV reflection and blue fluorescence while increasing brightness at 650 nm. and improving the color fastness of the garment.

One of the most exciting implications of this work is that, free of brightness from 450 nm. down, blaze orange is an excellent choice of color for low visibility to deer. With effective hunter education, the use and therefore effectiveness of blaze orange could be dramatically improved. We are thrilled to be at the leading edge of developments that may ultimately save many lives.





This graph was obtained from a Perkin Elmer LS50 Luminescence Spectrometer by exciting one small bandwidth at a time. It demonstrates that treatment with U-V-KILLER eliminates the emission of luminescence (resulting from excitation at 10nm lower wavelength) in the UV and Near IR portions of the spectrum with no loss of luminescence in the human visible range, particularly the important 600nm Blaze Orange Peak.


This graph was also obtained from Perkin Elmer LS50. The graph illustrates the measured luminescence spectrum when the blaze orange sample is excited by the full spectrum from Xenon lamp source. Notice that the 369nm peak exhibited by the untreated sample is completely invisible to humans but falls in the area of UV that is strongly-visible to game animals. This peak is totally eliminated in the treated sample. The excitation energy is instead released by the treated sample at two peaks in the longer visible wavelengths not easily distinguished by game animals. The 600nm peak vital to the effectiveness of Blaze Orange to Human eyes is actually increased by treatment with U-V-KILLER.

These tests and actual observation in the field have proven that a hunter in blaze orange that has been treated with U-V-KILLER is more visible to other hunters but is no longer easily seen by game animals and birds. The U-V-KILLER treatment allows safer hunting and more successful hunting.

To this point we have focused primarily upon color vision measurements and their implications. This is very recent work. Most of what we know about the deer's sensitivity in low light (rod vision) predates the work at the University of Georgia and was eloquently summarized by Dr. Neitz in his letter of December 1989.

The following is that letter (which is summarized by the graph on the inside front cover) and a brief discussion of its implications for hunters.



December 21, 1989

Atsko Inc.
2530 Russell S. E.

Dear Mr. Gutting

In response to your inquiry about the visual capabilities of game animals, I have attempted to compile the current scientific knowledge with a minimum of specialized jargon.


Grazing animals depend on keen vision at dawn, dusk and night in order to survive. Their eyes are specialized to see best under very low light conditions in which we can barely see or cannot see at all.

The extraordinary capability of grazing animals to see in dim light (and even almost no light) is because:

1) Their pupil can open wider to admit more light. Since it is the total area of the pupil that is important, the light gathering power of the eye increases as the square of the pupil diameter. Thus, an eye of about the same size as the human eye with a pupil that can open to three times the diameter of the human pupil gathers 3^ or 9 times more light. (Note that it is not the eye size that is important for visual sensitivity but rather the size of the pupil relative to eye size. Large eye size is important, however, for good resolution of detail).

2) Vision is initiated when light entering the pupil strikes the retina-the light sensitive layer of tissue at the back of the eye that is analogous to the film in a camera. The retina contains two kinds of light-sensitive receptor cells, rods and cones. The cones are responsible for daytime vision and color vision. Rods are responsible for vision in dim light. Tne central region of the human eye (the fovea) on which we depend on most for vision is tightly packed with cones but contains no rods. The rest of the human retina contains both rods and cones. The ratio of rods to cones increases in the periphery of the human retina.

Ungulates (hoofed animals) also have both rods and cones but rods predominate (even in the central area) making up well over 90 percent of the total photoreceptors over the entire area of the retina. The rods are incredibly sensitive to light-about one-thousand times more sensitive than cones. The high ratio of rods to cones in the eyes of ungulates makes them very sensitive to dim light and especially sensitive to shorter wavelengths of light as described below.

3) Ungulates, cats, dogs, and predators have a reflective layer in back of the retina that greatly enhances sensitivity. This reflector is called a reflective tapetum. We see the effect of the reflective tapetum as "eye shine" in animals. Human eyes don't shine at night because light that transits the retina without being absorbed by a photoreceptor cell is lost, absorbed by a black layer (the pigment epithelium) at the back of the eye. The effect of the tapetum for the animal is that light that passes through the retina without activating a photoreceptor the first time is "recycled"-reflected back to the photoreceptors for a second chance.

4) The human lens contains a filter that blocks U.V. light from reaching the retina. The U. V. filter in the human lens has a yellow appearance and also absorbs heavily in the violet and blue. This filter is not present in the lens of ungulates. They receive much of the U. V. light that we filter out.

In daylight, vision is based on cones that are most sensitive to middle and long wavelength lights. The yellow filter in our lens probably serves two purposes. First short wavelength light (blue, violet, and U. V.) is scattered and refracted much more in the eye than long wavelength light (yellow, orange, and red). If it were not filtered out by the lens the short wave light would fuzz the retinal image slightly and interfere with our ability to see fine detail. Expert marksmen know that acuity can even be further improved by wearing glasses with yellow lenses that block more blue light than the human lens. The other purpose of the U. V. blocking filter in the human lens is that it appears to protect the retina from U.V. damage. This damage probably progresses very slowly over decades of life, so protection is less important for animals with much shorter life spans than humans. As daylight fades to night, light levels drop below the threshold for cones and vision depends on rods. Unlike cones that are sensitive primarily to longer wavelengths the rods are most sensitive to shorter wavelengths. This transition from long wave sensitivity to shortwave sensitivity that occurs during dark adaptation is termed the Purkinje shift. The rod sensitivity is highest to wavelengths near 500 nm (the blue green region of the spectrum). Rod sensitivity drops off quickly for wavelengths longer than 500 nm, but stays fairly high for wavelengths shorter than 500 nm, even into the ultraviolet.

The price that humans pay for protection from the U. V. light and slightly higher acuity in day light that is provided by the U. V. blocking filter is an extreme loss of sensitivity to much of the spectrum where rods are sensitive. 400 nm is the wavelength that is usually considered to be the break point between visible and ultraviolet light. This is because the average human lens absorbs 94% of the light at 400 nm and its absorption increases dramatically for wavelengths shorter than that. We do not see U.V. because it never reaches the retina. Animals without the U. V. filter have an enormous advantage over humans in ultraviolet sensitivity. For example, rod sensitivity is still fairly high to U. V. light with a wavelength of 380 nm (long wave U. V.). The lens in the human eye blocks over 99% of this light. This means that based on this factor alone eyes that don't block U. V. will be over 100 times more sensitive to 380 nm light than humans.

One can easily see that with all these factors multiplied together, under many conditions, ungulates are expected to see hundreds of times better in dim light than humans. Under some special circumstances their advantage is even much greater. A distant object reflecting U. V. light whose image fell on the central region of the retina would be an incredible million times more visible to a carnivore or ungulate than it is to a human.

Humans are much better visually equipped than any game animal to read the fine print on a topo map at noon on a sunny day. But game animals are thousands of times better equipped to see objects that reflect short wavelength light under dim conditions.

Birds-Many birds are also sensitive to U. V. light. Their lenses also lack a U. V. filter. But,their sensitivity to U. V. comes about for a much different reason than in ungulates. Most birds are active in day-light and their retinas have a high concentration of cone photoreceptors. However, they have a type of cone photoreceptor that is not present in humans-a cone that is specifically sensitive to U. V. light. Scientists believe that many birds may actually see U. V. light as a separate color that is different than any of the three primary colors seen by humans.


The ability to see color is an important aspect of human vision. Color differences often allow us to easily identify objects from their backgrounds that would otherwise be invisible. For example, at a distance, ripe red tomatoes on the vine are much more easily seen among the leaves than unripe green ones.

Humans are able to see color because of three different types of cone photoreceptor cells in the retinas of their eyes. One cone type is most sensitive to short wavelength (blue) lights a second is most sensitive to middle wavelengths (green) and a third is most sensitive to long wavelength (red) lights. The three different cone types are the basis for what has been termed trichromatic (literally three-color) vision in humans. It should be noted as an aside that the majority of the cone photoreceptors in the human retina are the long-wavelength sensitive type, the middle wavelength sensitive type are the next most common, and the short wavelength sensitive are rare-only about 10% of the cones. The blue sensitive cones are important for color vision, but because of their small number they provide little or no overall sensitivity to short wavelength light.

Sincerely Yours,

Jay Neitz, Ph. D.
Vision Scientist



Scientists have studied color vision capacities in a number of animals. Among mammals, only primates (monkeys and apes) have been found to have trichromatic color vision like that of humans. However, a number of other mammals have color vision that is based on only two different cone types; this is dichromatic (two-color) vision. This simplified type of color vision seems to be common among mammals and has been observed in carnivores (e.g. dogs and cats) and ungulates (hoofed mammals). Although vision is predominantly based on rods in these animals (more than 90 percent of the total photoreceptors in their eyes are rods giving them excellent night vision), they have enough cones to provide color vision. Obviously color vision based on only two different cone types is not going to be as good as human color vision that is based on three types. The deficiency in dichromatic color vision is in the ability to discriminate among the colors of objects that reflect light in the middle to long wavelengths, i.e. green, yellow, brown, orange, and red. The ungulates and carnivores with color vision based on only short wavelength sensitive cones and long wavelength sensitive cones, would find these colors difficult or impossible to distinguish. However, for theseanimals, blue, violet and near ultraviolet (which is invisible to us because it is blocked by the lens) stand out from the other colors. The colors of earthly objects are mostly browns, tans, greens and yellows. To an animal with dichromatic color vision, a sportsman wearing garments that strongly reflect short wavelength light would stand out against these backgrounds like a ripe red tomato on a green vine.

The scientific report from Dr. Neitz summarized by the graph on the inside front cover overwhelmingly confirms our observations and explanation of the way in which game animals see. Game animals, birds, and insects have certainly evolved a wide range of visual capabilities to spot predators. The art of camouflage is complex, varying with season, location, time, weather, activity, surroundings and observer. One conclusion is obvious, U. V. brighteners are a real stand-out to game animals in the Wild. Your camo and exposed clothing must absorb rather than reflect U. V. light.

Using U-V-KILLER on my camo in 1990 for the first time I was astounded with my success. While having hunted for years, I have never considered myself an expert. I lack patience, am always fidgeting on my stand and move too fast while stalking, but that season was an eye opener. I took a 140 pt. Whitetail buck with a rifle, 5 bucks, (two in Michigan, 3 in South Carolina) and one doe and 3 javelinas with the bow. No, I did not spend months hunting, the fact is that I had less time that year and only had 5 days in Michigan, 4 days in Texas, and 8 weekends in South Carolina. I actually saw more deer in my time afield than I had seen in the previous 5 years. I was also able to get much closer to the deer I arrowed than ever before, and believe me I need to get within 25 yards.

The most astounding result of the treatment of my camo with U-V-KILLER has been how much movement I have been able to get away with. We have all experienced how our eye catches or is attracted to anything that moves. When our head is still, and we are looking out across an opening, we instantly see a bird flitter from one seed stalk to another at 200 yards. Game animals are able to detect movement even better than we are. We can catch, out of the corner of our eye, movement in our peripheral vision. We are unable to identify what moved until we turn our eye or head to focus on the subject. This is because we humans have a narrow field of vision, about 3 degrees, on which we are able to focus sharply, and our peripheral field of vision is approximately 180 degrees.

Deer have a much broader field of vision on which they are able to focus sharply, and their peripheral field of vision in which they can detect movement is over 300 degrees. This physical superiority gives the deer an advantage in detecting movement over a much wider field of vision and they are also able to immediately focus upon and identify objects in a wider field of vision.

We have all had the experience of having a deer run off when we tried to stand up or raise our rifle or bow. Imagine how easy it is for the deer to see you move when your camo is as bright and reflective as blaze orange is to our eyes. Camo treated with U-V-KILLER is not bright and therefore blends in with the natural background. You are harder to see when you move, and if you move very slowly, you have an excellent chance of getting away with it.

I was able to slowly draw on two deer at 25 yards while they were looking in my direction.

If you are an average deer hunter you are approximately 12% successful in harvesting a deer every year. With all of the modern weapons at our disposal, scents, and computer designed camo patterns, plus the fact that there are many more deer today, something is very wrong. An Indian of equal success would have starved to death. However, the Indian, like the early American, had something more going for him. There were no brighteners in his clothing. He did not glow, his garments were made of natural materials that were never dyed or washed with fluorescent brighteners.

I had often observed that northern guides are very successful in stalking game animals. The one thing they all had in common was the wearing of woolen garments in plaids, browns and greens. They washed their woolens in Woolite® (which has only recently added brightener) or dry cleaned them, and they blended in because they did not reflect U. V. light.

You can observe, for yourself, the effect of brighteners on your own camo, if you have access to a U. V. bug light. Simply hold your camo under the light and see if it brightens, spray it with U-V-KILLER and watch the brightness disappear. This is not magic, it's technically simple, you are covering the reflective dye with a blocking dye, and if you have a bug light, you can watch it happen.

Where and Why We Have U. V. Brightening Dyes

The Brightener dye content in detergents and new cloth has steadily increased since first introduced as blueing after World War 2. These dyes protect the cloth from Ultra Violet degradation or sun rot. They also make textile colors look brighter and whites look whiter. Every introduction of a new and improved detergent has contained more and better brightening dyes. All of the new textile blends introduced in the last 50 years have been treated with more and more of the brightening dyes. Today there are over 200 U. V. brightener dyes available. As U. V. glow became common, the game animals learned to respond to it just as they would to the smell or sound of the hunter. If it glows, it's a human and the bigger the buck, the less chance you have of seeing him if you glow.

U. V. Brighteners and U-V-KILLER on Blaze Orange

U-V-KILLER is equally effective on Blaze Orange. Humans are unable to observe this effect because our eyes are overpowered by the bright Orange to which we are so sensitive. Blaze Orange has been chosen by governments as the international safety color because it is the one color that we humans see the best against any background. Blaze Orange falls into the spectrum at 600 nm which is near the peak of human sensitivity, it is also the only color to which our eyes are more sensitive than the deer (a graph of the ungulates sensitivity to the light spectrum is on the front cover). Blaze Orange is so bright to our eyes because a fluorescent brightening dye has been added to the Orange pigment. This causes the reflecting, glowing quality, that makes it so brilliant to our eyes. This is the same effect the U V Brightening dye has on our clothing when seen by the deer. Except the deer is seeing a bright glowing blue. This brilliant blue color is out of place in nature and stands out just as much to the animals as Blaze Orange does to our eye. While we humans are more sensitive to the reds and oranges in the longer wave lengths, the animals are more sensitive to the shorter wave lengths of light. The vision and environment of man are a perfect combination for seeing International Orange, just as the vision and environment of the deer is ideal for detecting U. V. fluorescent brighteners.

How animals see Blaze Orange is complex because it depends on the light conditions and whether the animal is using his cones in daylight or has switched to rod dominated vision which is referred to as the dark adapted eye. We humans have a similar switch to rod dominated vision. On a moonlit night, away from artificial light, all we see is a black and white world in shades of gray.

In low light conditions, the effect of Blaze Orange is easy to understand, when comparing the dark adapted eyes of humans and animals. Both are seeing only shades of gray (rod dominated function) but the game animals eyes are thousands of times more sensitive to the available light source (a graph showing U. V. Light as the dominate component of available light at different times of day appears on the inside back cover). Blaze Orange will appear as a shade of gray to animals like the deer if there are no Ultra Violet Brighteners present on the Blaze Orange clothing. When U. V. Brighteners are on top of the Blaze Orange pigments, the color seen by the deer will be a highly reflective bluish white glowing color, as bright and as out of place in nature as Blaze Orange is to you on a bright sunlit day. This situation occurs at night, at dawn and dusk, and in deep shaded forests on cloudy days; whenever the available light allows the eye of the deer to shift to rod dominated vision.

Animals like the deer prefer to function in lower light for superior vision. They see better in low light because their eye is rich in rods and deficient in cones. It is not often that we observe any game animals actively feeding and moving about in bright sunlight. They prefer shaded areas and cloudy overcast days. We humans are the opposite, we are more comfortable using our cones, (daylight vision) as we have few rods and none at all in the fovea, the area in the eye responsible for our sharpest vision.

Daylight vision of Blaze Orange is more complex. Ungulates like the deer have two cones (in limited concentration). These give him limited dichromatic color vision similar to a human with protanopia, red-green color blindness. They perceive blues and yellows, but are unable to distinguish green, yellow, orange, red, tan, brown, and gray from different shades and intensities of yellow. In simple terms deer see their entire world, in full daylight, as shades of yellows, except for a blue sky, blue water, and a few blue flower petals. Even Blaze Orange is just another yellow UNLESS IT IS COATED with an Ultra Violet Brightening Dye. The U. V. Brighteners cause a very powerful stimulation to the deer's blue cones, which, when added to the stimulation of the yellow cones results in their seeing a BRIGHT WHITE. This bright white stands out against their natural world as a powerful signal, or warning just as the Blaze Orange does to the human eye.

When you treat your Blaze Orange garments with U-V-KILLER you stop the fluorescence of the U. V. light. You cannot see the effect because the human eye is overpowered by the Blaze Orange brighteners. Your Blaze Orange is still protecting you from other humans but blends into the deer's yellow landscape (see pages 10 and 11).

With U-V-KILLER on your Blaze Orange you are safe and legal.

H.E.A. Recommendation for Blaze Orange



U-V-Killer stops ALL the

Ultra Violet light reflection and glow on all your clothing, Blaze Orange or Camo, and stops you from glowing in daylight, at dawn and at dusk, in deep shade, and at night. You blend into the animals' daylight world and their twilight world.

You will observe more animals because you will have a better chance at remaining unseen.

It does no good to treat only part of or some of your garments. Everything you are wearing must be treated. Hats, gloves, face masks, socks, etc. Otherwise the one brightly glowing item will give you away. A very important point to remember is that if you wash your U-V-KILLER treated garments in SPORT-WASH, the U-V-KILLER treatment will last for at least six washings. On many fabrics the treatment will last for years, but, if you wash your treated garment in another detergent you will again dye the garment with brighteners. You will then have to retreat the garment with U-V-KILLER.

It makes no difference whether you are a beginner or the most successful hunter in the woods. When your clothes stop glowing you are going to be more successful and have more opportunities.

In order to be able to treat everything a hunter takes into the woods, we have a product for blocking U. V. reflection on bare metal, wood, and painted surfaces. Called U-V-SHIELD it may also be brushed on hard fabric like snake leggings and treats items like backpack frames, tree stands, arrows, quivers, duck decoys, etc.

Complete instructions on how to apply U-V-KILLER and U-V-SHIELD are included with the product and should be read thoroughly before using (also see page 24 & 31).

The Sense of Smell

Odor control is a major concern for hunters and fishermen. Until recently commercial and home odor control products were inappropriate for their use. Available products have focused on making things smell good rather than odorless. Research centered on eliminating bad odors by creating a new odor that was not objectionable. Clothes, carpets, commodes and companions are all made to smell good, clean and fresh but never odorless. The cover scent is just stronger than the objectionable odor it is blocking out. Many hunting and fishing odor control products use the same method. They try to block the human odor with cover scents like apples, skunks, fox and buck and doe urines.

We cannot tell you what animals smell. We know that deer are 10 thousand times as sensitive to odor as humans. A large fraction of their brain is devoted to olfaction (the ability to smell) and scientists say deer are able to recognize six different odors at the same time. Certainly their marking of territory and other behaviors indicate that they readily smell things we are unaware of.

We know they can tell the difference between a rotten apple from North Carolina and one from Pennsylvania. This suggests that cover, attractants, and other artificial scents are readily recognized as foreign and function only through the inquisitive nature of animals. Any attempt to fool them may be as appropriate as a child trying to trick Einstein with a riddle in relativistic physics. Fish may have even a more highly developed sense of smell. Sharks have shown their ability to detect a few parts per billion of blood in water at a distance of several miles. Salmon find their spawning streams by odor at great distances. Bass following a lure, attracted by its motion or vibration turn away when they smell a contaminating odor. So how can a cover scent work?

Our approach is to simply reduce the odors of the hunter and fisherman to the lowest possible level without introducing any new odor. Having no odor means no detection by game or fish.

Some products are available that use this method but do not have the technology to do the job. Their main ingredient is baking soda and/or washing soda with one or more antimicrobials added so nothing grows in the bottle. Baking soda raises skin pH to slow the growth of bacteria that cause body odor but despite its reputation in the refrigerator it actually absorbs very little odor before it reaches equilibrium and releases odor molecules faster than it reacts to new ones. These products are only partially effective at best and are a poor value for the few cents worth of ingredients in deionized water.

In order to study and judge the effectiveness of different materials for odor control we had to create standard smells and develop a rating scale. Then we perfected test methods that gave consistent and reproducible results. The most sensitive observers were young non smokers who favor a bland diet.

We tested every viable material available. We tested wet and dry systems against a wide range of common odors. We found two ways to eliminate odor without introducing a new odor. The first method is by oxidation and the product is N-O-DOR the liquid spray. The second method is selective adsorption and the product is N-O-DOR II the powder.

N-O-DOR & N-O-DOR II are not fully compatible. Clothes that are heavily powdered with N-O-DOR II will deactivate N-O-DOR liquid. There are applications where either system could be used. However some problems are better suited to the liquid application and others are best handled by the powder.

What is N-O-DOR the liquid, it is an oxidizer, a new application of natures own process for destroying organic wastes. You are familiar with how chlorine destroys odor and bacteria. Chlorine is an oxidizer. Oxidizers combine with organic compounds and change them to non-volatile salts. The change is permanent and they no longer smell. The problem with chlorine is that it has its own odor. You recognize the smell of chlorine when you are close to a spa or swimming pool, sometimes you can smell it in drinking water. We found a new oxidizer that was developed for the food industry. It has no odor of its own, but like chlorine permanently destroys all odor caused by organic compounds and is safe for you to use on your skin. Do other products say you can use them on your skin? Mixed N-O-DOR lasts for 30 days in its spray bottle because the oxidizers are released only as needed.

The two separate packages of concentrate have years of shelf life and activate only on mixing in water. This unique package system makes it possible for the hunter or outdoorsman to achieve on the spot odor control conveniently and economically. N-O-DOR does not eliminate the need of washing your clothes & body, it provides a way to remove every trace of odor from your clothes & body while in the field. It is in fact a shower in a bottle. Spraying your body from head to toe deodorizes so you feel as refreshed as if you had taken a shower.

Our body odor is the result of accumulating waste products from bacteria that live on the skin. Heavy accumulations must be washed away from our clothing and skin. This is done with Sport-Wash unscented, non-brightening laundry detergent and Sport-Wash unscented Hair & Body Soap.

The molecular structure of the remaining organic material that causes odor is safely changed by chemical reaction to form an odorless compound. This Oxidation-Reduction process permanently eliminates all odor from all organic material. As more organic material is generated N-O-DOR continues to oxidize it until it all dries away.

Ideally, the hunter should begin each day with a shower using Sport-Wash unscented Hair & Body Soap. When this is not possible one should spray on N-O-DOR liberally, ON THE SKIN AND THE HAIR, then dry off before dressing in clean clothes. If clean clothing is not available be sure to spray clothing with N-O-DOR and allow to dry. After the exertion of traveling to the stand or blind N-O-DOR can be re-applied. As the day progresses and perspiration persists, additional N-O-DOR can be applied to the skin and clothing as needed. With N-O-DOR you are able to remain scent free all day. Nature has always cleaned up her spent organic debris by oxidation. Now, thanks to the experts at Atsko, you can be odor-free and a more successful hunter.

N-O-DOR will also destroy odors in your car, home or wherever a problem exists.


1. Will U-V-KILLER, on my camo, cause skin irritation?

No. U-V-KILLER will not cause skin irritation unless someone is allergic to the dyes used on all clothing. When applying U-V-KILLER, wash your hands when you are finished as there is no advantage to treating your skin.

2. Will U-V-KILLER cause my camo to fade or discolor?

No. It will in fact protect your camo from fading caused by ultra violet radiation. U-V-KILLER is specifically formulated to be compatible with the dyes and fabrics used in the manufacturing of clothing.

3. What effect, if any, does U-V-KILLER have on the cloth?

With most fabrics there is no difference in feel, or hand as it is called in the textile industry; some fabric may feel slightly stiffer after drying but this slight stiffness disappears quickly with wearing. If you want to eliminate this slight stiffness quickly before wearing, simply put the garment in your clothes dryer and tumble it with no heat for 15 minutes.

4. Does U-V-KILLER treat the inside of the garment when I spray it on the outside?

No. You must spray the inside of lapels and pocket flaps to insure full treatment.

5. How durable is the U-V-KILLER treatment, and do I have to retreat my camo, and if so how often?

On cotton garments U-V-KILLER lasts forever, as long as you wash your camo in SPORT-WASH. If you wash in Tide, Cheer, etc, you will have to retreat with U-V-KILLER as you have redyed the cloth with brighteners. Synthetic fabrics last anywhere from 12 to 18 washings and then the garment must be retreated with U-V-KILLER. So it is a good idea to retreat every season or two. Normal wear out of doors, rain, snow, etc., will not affect the U-V-KILLER treatment. It only wears off on some synthetics in the washing machine.

6. Can I treat my clothes with a waterproofing spray like SILICONE WATER-GUARD after using U-V-KILLER?

Yes. Waterproofing sprays work and have no effect on U-V-KILLER.

7. How does U-V-KILLER affect waterproof garments?

Waterproof materials are still waterproof and breathable. U-V-KILLER does riot cause any problems to seams, threads, or glue joints on any synthetic fabrics.

8. I've treated my camo and I still see a blue glow with my U-V lightsource. Does this mean that it is not working?

Two possibilities exist. First you may be seeing only visible blue and assuming it is U. V. U-V-Killer does not block visible blue because blocking it would change the appearance of your camo in the visible spectrum, (We assume that you chose a pattern & color that are right for the terrain you hunt). The U. V. lightsource, even the flashlight we sell, has some visible violet wavelengths present and if all U. V. is absorbed you will still see some of this visible violet. If you place a single drop of U-V-Killer on a piece of brightened white paper or cloth and check it with the lightsource, you will see a dramatic difference because the brighteners are seen more on white. This demonstrates how effectively the absorber in U-V-Killer is working. You may be assured that a good application of U-V-Killer is just as effective on your camo.

The second possibility is that the application wasn't sufficient. Excess brighteners on the cloth will float to the surface of the U-V-Killer treatment. These excess brighteners must be removed by first washing with Sport-Wash. Wash twice if in doubt. Clean old detergent residue (which is full of brighteners) from washer by washing non-camouflage clothing in Sport-Wash before washing your camo. Be sure to dry your camo (according to the label instructions) before treating with U-V-Killer. When applying U-V-Killer imagine you are applying a light coat of paint to the exterior surface. You want to cover every thread. If the spray is leaving spots, gaps, or streaks use a small brush, cloth, or even your hand to spread it back and forth. A bubbly white froth will remain visible up on the surface for a few minutes so that you can see that the coverage is complete. When dry you can check your progress with a blacklight. To properly check your camo under blacklight you must use a true Ultraviolet fluorescent light source. There are at least three domestic manufacturers of Ultra-Violet tubes, for example- General Electric "BL",Westinghouse "BL", and Sylvania "Blacklight 350". These blacklight tubes have radiation peaks at 350 nanometers. They will activate brighteners (like Tinopal by CIBA GEIGY) which are common in detergents. There are also on the market U-V tubes which have a blue filter to block visible wavelengths, they appear blue and are marked "BLB". Filtered sources, like the portable light we sell for $19.95 make it easy to see the brightener effect because there is less visible light present to confuse the observer. A true U-V lightsource will enable you to make a complete check of all your hunting gear and provides a way to double check yourself once you have treated your equipment with U-V-Killer products.

9. Will U-V-KILLER change the appearance of my camo? Will it look any different to me?

No. All colors and camo will look the same to you in full daylight.

10. Will U-V-KILLER crack or peel off at high or low temperatures?

No. U-V-KILLER forms a permanent bond unless applied to water-proofed fabric.

11. Is U-V-KILLER flammable?

No. In fact you can put out a fire with it.

12. What about odor? Does U-V-KILLER have any lingering scent?

No. U-V-KILLER is scent free when dry.

13. Will U-V-SHIELD work on outdoor items that are exposed to severe weather?

Yes. U-V-SHIELD is a clear weather proof coating that works great on items as exposed to the elements such as duck decoys.

14. Can I still spray my hunting clothes with a scent killer like N-O-DOR?

Yes. U-V-KILLER has no effect on N-O-DOR or how it works.

15. Does Atsko make anything to make my Gore-tex jacket waterproof again?

Yes. When your jacket was new it probably shed water because of a factory applied Teflon treatment on the outer shell. Contamination from wearing and residues of other detergents have made that repellent ineffective by providing pathways for water to wet through it.

Wash the garment in SPORT-WASH according to manufacturers recommendations. This will remove all residues and surfactants. Now iron the shell at the highest setting allowed by the manufacturer and the waterproofing will work like new again. If there was no factory waterproofing treatment, you can waterproof the garment with our Silicone Water-Guard.



Light is not as uniform or as simple as it appears.

Our inside back cover illustrates some of the many variations in the content of natural light. In general, the longer wavelengths are maximized in early afternoon sunlight, while the short wavelengths, (Ultra Violet light) dominate in shade, at dawn, at dusk, and at night, and are further enhanced on overcast days. In general longer wavelengths are limited to straight line propagation and are readily absorbed as heat, while short visible and Ultra-Violet light scatter-reflects through our atmosphere, making the sky appear blue, and filling in the shadows. Animals have evolved to see in Ultra-Violet light because it dominates their environment, particularly in the hours they are most active.



U V brighteners on the hunter's pants cause a startling luminescence that attracts the attention of game animals and insects. The bright blue glow is unnatural and in sharp contrast to the world of yellows (daylight vision) or grays (dark adapted eyes at dawn, dusk, and in shade) in which deer live.

After treatment with U-V-KILLER, blaze orange appears to the deer as just another shade of pale yellow (daylight eye) or gray (dark adapted eye), however the bright glow of the UV brighteners in the untreated blaze orange allows deer to spot you easily in full light or at dawn and dusk. To the human eye the treated blaze orange is even brighter and keeps you from becoming a target for another hunter.

As light levels decrease in deep shade and at dawn and dusk, color vision is lost, but the advantages of the animals' eyes (already tens of thousands of times more sensitive to UV brighteners than ours) now combine with the increased UV content of the available light. [ see graphs at right ]

Birds: Birds see our full spectrum of colors, but they have an additional receptor for Ultra Violet light. They see everything we see, plus the UV spectrum we do not see. Anything that reflects or luminesces UV light stands out and alerts them like a neon sign.