the invention relates to side - scattering light guides that generally comprise a core of transparent optically homogenous material seeded with diffuser particles . the light guide also comprises an optically transmitting sheath , having a lowerrefractive index than the core , surrounding and in contact with the sides of the core to prevent any light being transmitted along the core from escaping through the core &# 39 ; s sides . in general , the diffuser particles impart only a small deviation to light rays incident upon them , and are distributed to scatter light being transmitted along the core so that at least some of the scattered light exits the sides of the core . a diffusing jacket is arranged to intercept scattered light exiting the sides of the core .