ShadowAce

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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 U-V 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

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

Much has been written lately about how U-V 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 U-V brighteners, we are talking about a time and place where U-V 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 U-V brighteners. As we move to dusk, dawn, deep overcast, or shade the absolute amount of U-V and short blue light decreases, but the fraction of total light contributed by U-V 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 U-V 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 U-V he may want to match this intensity just as he would try to match the lack of U-V from a tree trunk or grass.

Now lets consider what a U-V brightener is. There are about 200 compounds in a handful of families that absorb light energy in the U-V 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 U-V damage and the whitening agents in cloth and laundry detergents generally release the energy they gathered through the U-V 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.

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