New direct measurement of high optical attenuation ratese in polar bear hairs -- 2-8 dB/mm in the visible -- and reanalysis of the data of Tributsch et al. [Sol. Energy Mater. 21, 219 (1990)] seem to rule out the UV waveguiding proposed by Grojean et al. [Appl. Opt. 19, 339 (1980)]. The case against fiber-optic polar bear hairs is summarized, and four conditions are given that any variation of the model of Grojean et al. would have to satisfy.
D. W. Koon, "Is polar bear hair fiber optic?", Appl. Opt. 37 (15), 3198-3200 (1998).
I must object to the title of the article, "Butterfly Thin Films Serve as Solar Collectors" (Miaoulis and Heilman 1998). The authors analyze the optics of iridescence in some species of butteflies and moths, but they fail to prove that the thin films that cause this iridescence behave anything like solar collectors.....In fact there is no need for a thermoregulatory explanation for the optics of Morpho and others. Camouflage, courtship, and display (Ghiradella [Appl. Opt. 30:3492-3500] 1991) probably suffice to explain why some butterflies are so shiny.
D. W. Koon, " Comment on 'Butterfly thin films serve as solar collectors'", Annals of the Entomological Society of America 92 (4), 459 (1999).
We measured the visible reflectance spectra of whole wing sections from three species of iridescent butterfles and moths, for normal incidence, integrated over all reflected angles. In this manner, we separated the optics of the thin films causing the iridescence from the optics of the rest of the scale. We found that iridescence reduces solar absorption by the wing in all cases, typically by approximately 20% or less, in contrast to claims by Miaoulis and Heilman [Ann. Entomol. Soc. Am. 91, 122 (1998)] that the thin-film structures that produce iridescence act as solar collectors.
D. W. Koon and A. B. Crawford, " Insect thin films as sun blocks, not solar collectors", Appl. Opt. 39, 2496 (2000).
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