<P> The 3M company developed a system based on optical lighting film and developed the 3M light pipe, which is a light guide designed to distribute light uniformly over its length, with a thin film incorporating microscopic prisms, which has been marketed in connection with artificial light sources, e.g. sulfur lamps . </P> <P> In contrast to an optical fiber which has a solid core, a prism light guide leads the light through air and is therefore referred to as hollow light guide . </P> <P> The project ARTHELIO, partially funded by the European Commission, was an investigation in years 1998 to 2000 into a system for adaptive mixing of solar and artificial light, and which includes a sulfur lamp, a heliostat, and hollow light guides for light transport and distribution . </P> <P> Disney has experimented in using 3D printing to print internal light guides for illuminated toys . </P>

Why is light not visible through a bent pipe