Why do fiber optic light guides lose so much energy?

Glass fiber optic light guides have several characteristics that contribute to loss in transmission. The most common are cladding loss between the core and cladding diameters, packing fraction loss due to gaps between individual fibers and fresnel losses due to reflections of the end faces. Additional factors include extreme bends over long durations, glass fracture cracks due to bending, and cross-talk between individual fibers. Typically, the total effect is a transmission loss of 6% per foot (visible light) with an illuminator-to-light guide coupling loss of approximately 30%.