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 lower refractive 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'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.