Total Internal Reflection

Total internal reflection occurs when light is passing through a medium (e.g. glass, water or plastic) with a higher index of refraction than the index of refraction of the medium (e.g. air) outside this material. For certain angles of incidence for light striking the boundary between the two and going from medium 1 to medium 2, light will not pass through the boundary but will be totally reflected inside medium 2. This occurs primarily when the light strikes at a shallow angle on the boundary. For a thin material of medium 2, like a fibre, these angles will always be small, and the majority of the light will stay inside the fibre.
Though widely known, the principal was demonstrated in 1870 by John Tyndall when he shone a light at a spout of water as it gushed out of a tank. The water fell in an arc and the light also traced the arc. The invention of modern fibre optics is credited to Narinder Kapany in 1955 during his time at Imperial College, London. During the 1960's early fibre optics were developed as a means of transmitting messages as an alternative to electrical wires and by 1970, the Corning Company in America produced the first practical fibre optic cable. It could transmit light about a third of a mile before most of the light was absorbed.
Optical fibre can reflect light of all wavelengths. Short wavelength light can carry the most information but longer wavelength light is affected by Raleigh scattering within the fibre.
Reflecting road studs also use total internal reflection to bounce back light towards incoming cars. Many road signs shine brightly in car headlights as they are covered in tiny transparent beads. The beads reflect light back into the direction that it came.