An illumination system (100, 200), comprising: at least one light source that generates light having at least one wavelength between 200 nm and 2000 nm; at least one low-scatter light-conducting optical fiber having an input end optically coupled to the at least one light source and having an output end, and configured to provide the light received by the at least one light source to the output end as guided light; at least one light-diffusing optical fiber having a glass core, a cladding surrounding the core, and a plurality of nano-sized structures situated within said core or at a core-cladding boundary, and further including an outer surface, and an input end optical coupled to the output end of the at least one low-scatter light-conducting optical fiber, wherein the at least one light-diffusing optical fiber is configured to receive the guided light from the low-scatter light-conducting optical fiber and scatter the guided light via said nano-sized structures away from the glass core and through the outer surface, to form a light-source fiber portion having a length over which the scattered light is continuously emitted; and a mirror having a focal spot or a focal line, wherein the light-source fiber portion is arranged at the focal spot or along the focal line; wherein: the at least one light source comprises first and second light sources that generate first and second light; the at least one low-scatter light-conducting optical fiber comprises first and second low-scatter light-conducting optical fibers respectively connected to the first and second light sources; and the at least one light-diffusing optical fiber is optically connected to the first and second low-scatter light-conducting optical fibers so that the first and second light travels in opposite directions as first and second guided light through the at least one light-diffusing optical fiber. at least one light source that generates light having at least one wavelength between 200 nm and 2000 nm; at least one low-scatter light-conducting optical fiber having an input end optically coupled to the at least one light source and having an output end, and configured to provide the light received by the at least one light source to the output end as guided light; at least one light-diffusing optical fiber having a glass core, a cladding surrounding the core, and a plurality of nano-sized structures situated within said core or at a core-cladding boundary, and further including an outer surface, and an input end optical coupled to the output end of the at least one low-scatter light-conducting optical fiber, wherein the at least one light-diffusing optical fiber is configured to receive the guided light from the low-scatter light-conducting optical fiber and scatter the guided light via said nano-sized structures away from the glass core and through the outer surface, to form a light-source fiber portion having a length over which the scattered light is continuously emitted; and a mirror having a focal spot or a focal line, wherein the light-source fiber portion is arranged at the focal spot or along the focal line; wherein: the at least one light source comprises first and second light sources that generate first and second light; the at least one low-scatter light-conducting optical fiber comprises first and second low-scatter light-conducting optical fibers respectively connected to the first and second light sources; and the at least one light-diffusing optical fiber is optically connected to the first and second low-scatter light-conducting optical fibers so that the first and second light travels in opposite directions as first and second guided light through the at least one light-diffusing optical fiber. the at least one light source comprises first and second light sources that generate first and second light; the at least one low-scatter light-conducting optical fiber comprises first and second low-scatter light-conducting optical fibers respectively connected to the first and second light sources; and the at least one light-diffusing optical fiber is optically connected to the first and second low-scatter light-conducting optical fibers so that the first and second light travels in opposite directions as first and second guided light through the at least one light-diffusing optical fiber.