Spectral Conformity—a Widespread Effect of Light

Abstract

WOOL¹, bleached by light, acquires some of its colour, becoming bluer in blue light or greener in green light. Reflectance and transmittance rise near the wavelength of the light because photons eliminate their particular absorbers, leaving the remainder of the chromophore unchanged. This phenomenon, which we named “spectral conformity”, was used, for example, in traditional wool bleaching by sunlight. Blue photons in daylight (spectral maximum in the blue^2–5) eliminate the absorbers of blue photons that made the wool yellow, thus making it bluer, and looking “whiter”. Cotton, linen, paper and so on, used to be sun-bleached. The question arises: is spectral conformity general or is it an interesting peculiarity of wool ?