Is polar bear hair fiber optic?
Polar bear hair does NOT behave fiber optically, either in the ultraviolet as originally claimed, or in the visible. This popular scientific myth has been propagated for over two decades by at least three teams of scientists [1-3] trying to explain why a polar bear's pelt appears black in the ultraviolet[4-7]. On closer inspection, the "fiber optic" claims made by three groups can be shown to be based on indirect, circumstantial evidence, and sometimes questionable interpretation of data. None of these three groups (nor any others) has yet claimed to have ever measured a significant amount of transmission of ultraviolet light -- say 1% -- through a significant length of hair -- say 1 inch. In fact, Tributsch et. al. have shown that transmission in the UV is much lower than in the visible. So if fiber optics explained why the bear appears black in the UV, the polar bear would appear black to our eyes as well.
In fact, my own lab measurements show that less than a thousandth of a percent of red light entering one end of a polar bear hair could travel the typical one-inch length. For ultraviolet light, the same amount of loss happens within, at most, one fifth the distance.
The bear's appearance in the UV can be explained by invoking the known UV-absorbing properties of the protein keratin, of which the hair is composed. Keratin is simply much more strongly absorbing in the ultraviolet than in the visible.
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Check out page of references to the literature of polar bear fiber optics
1. Grojean, R. E., Sousa, J. A., and Henry, M. C., "Utilization of solar radiation by polar animals: an optical model for pelts", Appl. Opt. 19, 339-46 (1980).
2. Tributsch, H., Goslowsky, H., Küppers, U., and Wetzel, H., "Light collection and solar sensing through the polar bear pelt", Sol. Energy Mater. 21, 219-36 (1990).
3. Alexis G. Clare, interview on National Public Radio's "All Things Considered", March 1995.
4. Lavigne, D. M. and Øritsland, N. A., "Ultraviolet photography: a new application for remote sensing of mammals", Can J. Zool. 52, 939-43 (1974).
5. Lavigne, D. M. and Øritsland, N. A., "Black Polar Bears", Nature 251, 218-9 (1974).
6. Øritsland, N. A. and Ronald, K., "Solar heating of mammals: Observations of hair transmittance", Int. J. Biometeor. 22, 197-201 (1978).
7. Reynolds, P. S. and Lavigne, D. M., "Visible and Ultraviolet Reflectance Characteristics of Arctic Homeotherms", Int. J. Biometeor., 25, 299-308 (1981).
8. Koon, Daniel W., "Is Polar Bear Hair Fiber Optic?", Applied Optics, 37, 3198-3200 (1998).
9. Bohren, Craig F. and Sardie, Joseph M., "Utilization of solar radiation by polar animals: an optical model for pelts; an alternative explanation", Appl. Opt. 20, 1894-6 (1981).
10. Bendit, E. G. and Ross, D., "Techniques for obtaining the ultraviolet absorption spectrum of solid keratin", Appl. Spectros. 15, 103 (1961).