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Shining a Light on UV Materials

by Drew Chicone
photos by Drew Chicone

In an attempt to bring some clarity to the muddy waters of fly-tying materials, and although I have no formal scientific training in this topic, I have spent a lot of time researching ultraviolet (UV) materials and the hubbub surrounding them. I have had some trial and error with my treasure trove of materials on the flats, and between that experimentation and my research, I’ll try to explain what fish might be seeing.

UV reflective materials do not react under a UV light. This means that particles of light in the UV spectrum that hit the material will be reflected and become more visible to predators that can see UV light. If no light is present, then there is no UV light either. If there is no UV light, then there is no UV reflection from the materials.

If birds, fish, and insects can see UV light, and humans cannot, materials that claim to be UV reflective cannot be tested with a blue light or a UV light since they simply reflect UV light, which we cannot see.

The visible spectrum shown in the colored portion of this diagram illustrates what is visible or can be detected by the human eye.Shorter wavelengths of light such as ultraviolet or (UV) light are not visible to humans and can only be seen by birds, insects, and fish.

Most but not all feathers are UV reflective. Some feathers reflect more UV light than others, such as jungle cock, peacock, and iridescent exotic bird feathers. However, birds in the ostrich family, owls, and hummingbirds have no UV reflective feathers at all. Bright-colored plumage and UV reflection may play a role in how these birds interact or communicate, especially when it comes to choosing a mate. UV reflective materials call attention to your fly against a dark non-UV reflective background and may trigger a strike. UV reflectivity matters most in low-light situations and at long distances in any direction, not just down. The farther away the materials can be seen, the better your chances are of attracting fish.

Colors like chartreuse and hot pink are automatically UV reactive and can be seen at a great distance underwater. They have proven to be productive colors for a number of species and have become standard choices for most saltwater attractor patterns.

White or lighter colored feathers are highly UV reflective, while darker or black feathers reflect far less UV light. White has the highest UV reflectivity, followed by blue, yellow, green, red, brown, and then black. Highly reflective UV colors like fluorescents are not typically found in nature, but they work well to get the attention of fish.

So what are you seeing when materials light up in the dark when you shine a UV light on them? These are UV reactive materials. UV reactive materials shine, radiate, incandesce, or fluoresce when you hit them with a UV light. Typically this means they have been dyed with UV reactive dyes. Highly UV reactive materials can be checked with a UV light. They gather light and fluoresce or luminesce in the dark. Materials that appear fluorescent in daylight absorb UV and reflect, or radiate, with a brighter intensity.

Peacock feathers are known for their iridescent qualities and are used as a fly-tying material in both freshwater and saltwater patterns. They are brightly colored feathers and are an excellent example of a UV reflective material.

One theory why highly UV reactive colors like chartreuse are so effective is that in some way they mimic blood in the water. However, blood does not react to UV light in the same way as UV reactive colors do. Many popular crime shows on TV portray blood as glowing when exposed to a UV light, but this is simply not true. In order for blood to glow, it needs to be treated with a reactive chemical, which makes the blood glow in the dark briefly even without a UV or black light. When exposed to UV light, blood absorbs the light but does not fluoresce; instead it appears black.

If a hemorrhaging baitfish appears black underwater, its image is a silhouette against a light background. Since most mortally injured fish float to the top eventually, its dark shape contrasts sharply against the brighter, sunlit backdrop. A silhouette is easily seen underwater at great distances, especially in stained or dark water. Again, the more visible a fly is, the better.

If you have spent any time scuba diving, you have probably noticed that some colors become less vibrant and eventually appear gray the deeper you go. This is because visible light can only penetrate so far in any direction, depending on the clarity of the water. This chart shows the estimated distance that visible and ultraviolet light can penetrate.

Each color fades and eventually appears gray at a different depth. UV light penetrates deeper in the water column than visible light does, so UV reflective or reactive materials are visible at greater distances. The colors of the visible light spectrum are gradually absorbed, depending on the color and clarity of the water. Colors with the highest energy, like red, orange, and yellow, disappear or dissolve to gray first and cannot be seen as you get deeper or farther away. This is important when selecting a fly or choosing the colors of materials for tying your next pattern. Not only do you need to take into consideration the color of prey you are trying to emulate, but you also need to consider the clarity of the water, the light conditions, and the depth that you will be fishing in. All these factors may affect how the fish sees the fly and ultimately how productive the fly is at attracting fish.

Visibility is much better in clear water than it is in cloudy, dark, or stained water. Clear water allows light, both visible and UV, to penetrate much more efficiently. The brighter the light, the better and farther away colors can be seen. Absence of light due to dark or stained water, time of day, or depth, reduces the depth and distance that a color can be seen. That is why on cloudy days, flies that have high contrast or a strong silhouette typically produce  better than a specific color of fly . . . which explains the old rule “Bright colors on bright days, dark colors on dark days.” It is a matter of getting something in front of the fish that can clearly be seen.

MidCurrent Fly Fishing
Drew Chicone is a fly designer, photographer, author, instructor, lecturer and materials expert whose passion for the sport has led him to the salty waters of Southwest Florida. He has lived and breathed the sport since he was tall enough to sit at the vise, and his fly creations are both well known and in high demand among Florida guides. Drew has been a FFF Certified Casting Instructor and commercial fly tier for many years. His patterns are sold in numerous fly shops and have appeared in many publications. Drew's other titles include Essential Bonefish Flies:Andros and Essential Permit Patterns. He is a member of theDyna-King Pro Tyer TeamandClear Cure Goo Pro Tyer Team, anAmbassador for Nucanoe, and a Royalty Tyer for the Orvis Company.
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  • Nymphermaniac

    Great article. Sheds a lot of light on the UV craze. Do you think a hot spot of blue or red is more effective on a trout fly? My friend says red disappears around nine feet and your graph pretty much affirms that. I always thought that in clear water that it was about three feet.

    • Brian Kozminski

      totally depends on the amount of suspended solids and turbidity. Blue/Purple travel further than red, although, we see red and ‘think’ it will perform better underwater, simply not true…

    • craig

      instead of a hotspot being color related, think of a hotspot as being contrast related. a brightly colored thread head on a dark fly provides an area of contrast, as does a dark thread on a light colored fly. beads accomplish the deed as well.

      • Nymphermaniac

        craig: My question was only in relation to UV. I use a lot of beads also and think they are great attractors. However, they don’t have anything to do with UV. On a recent trip for trout, I found that the use of UV dubbing made little difference on size 20 flies fished as nymphs or scuds in 3-6′ of water. The best producers were the “Blue or Purple Assassins”, with an 11-0, blue bead head.

  • UVRC

    A few corrections. Iridescent feathers typically reflect very little UV. Visible color has nothing to do with the amount of UV reflected. One yellow feather may absorb most UV striking it, another may reflect UV. For example, Golden Pheasant crest is what is known as an “honesty marking” for that bird species. The gold feathers are highly UV reflective when the bird is in its prime, but reflect little UV in an old bird. The feathers may appear identical to a human; however a female pheasant sees in the UV and knows that the strutting suitor is past his prime. Fortunately, most of our farm-raised birds are harvested in their prime and any UV properties are unaltered after death. This is because the UV reflectance of feathers (and a mayfly’s body and wings) is a function of the construction of the feather, not pigments.
    White marabou (turkey marabou) is often highly UV reflective. However, sometimes it is treated with TiO2 as a whitener and the TiO2 absorbs UV, making the bright white feather very dark in the UV.
    Natural light blue dun hackle has superb UV characteristics, as does natural grizzly. Dyed feathers OTOH, are always dependent on the pigments used in the dyes for their UV characteristics.

    Furs and hairs also have unique UV patterns.
    The percentage of solar UV light increases at dusk, just when the mayflies come out to dance. Mayflies depend upon their UV patterns to identify species and sex. (When you only are going to have one hot date, you want the species and gender to be right.)
    The rods in the trout retina – used for night vision – are more sensitive to UV than to visible light.
    Just some thoughts and corrections.

    • Brian Kozminski

      Thank you and WOW!! Love this, very cool and not just another little gimmick to make me repurchase everything in my tying arsenal….

      • UVRC

        You won’t need to buy anything new in tying materials, probably. You just need to know which materials reflect UV in what percentages and adjust your patterns accordingly. For example, most upright mayfly wings will have significant UV reflectivity, so do most natural white tail hairs (whitetail deer are able to see in the UV and use their tail for signaling in low light); so a Hairwing Royal Coachman makes sense, likewise the grizzly hackle tips of the Adams, etc..

        • Great input on a fascinating topic. Thanks, Reed.

          • UVRC

            More on iridescence. You can see from the images below that iridescent feathers are dark in the reflected UV. However, if you used the herl as a body and white duck or goose quill as a wing, you would have a potent combination (a.k.a., a Coachman, or Zug bug, or a Prince Nymph, etc.).

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  • UVRC

    Just another correction. The writer of the article above said: “Colors with the highest energy, like red, orange, and yellow, disappear or dissolve to gray first and cannot be seen as you get deeper or farther away.”
    Actually, the photon energy is the inverse of the wavelength, so violet has the most energy in the visible spectrum, and red has the least energy.

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  • UVRC

    The loss of the four small UV-specific cones is not significant in terms of the trout’s vision in the UV. All of the cones have a secondary peak in the ultraviolet. As the tiny UV cones disappear, the other cones increase in size and sensitivity, both to visible light and ultraviolet. see for a full explanation. Thanks.

  • Daniel D Holm

    Very nice text. I also have made this video about Uv and Fl.

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  • les rouse

    UV penetrates deeper in clear water but what about stained water . With its high energy wouldnt it be absorbed before colors in the visible spectrum , making fluorescent lures unable to emit that glow ?