Abstract: The opto textiles of the present invention utilize and exploit the light interaction characteristics of the fiber or yarn itself, and the light interaction characteristics of the fabric as a whole, such that the fabric presents a given appearance or provides a given visual effect, adequately cools a wearer/user, adequately heats a wearer/user, and/or fulfills a lifestyle or therapeutic function, for example. In various exemplary embodiments, the present invention provides fibers, yarns, and fabrics that manage and manipulate the properties of light, such as wavelength, propagation direction, degree of coherence, and intensity, utilizing, for example, the light-matter interaction, fluorescence, phosphorescence, photochromism, thermochromism, and heat-activated light generation, such that application-specific needs may be met.