Abstract: A fiber optic detection system in which a single optic fiber has a U-shaped configuration. A source of light is disposed at one upper free end of the optic fiber and a light detector is disposed at the other upper free end of the optic fiber. At the bottom of the optic fiber is a light variable loop adapted to be disposed in various media, such as liquids, fluids and air. The light from the source of light is conducted from the source of light through the optic fiber and to the light detector. The quantum of light lost as the light travels through the light variable loop will depend on the medium or the concentration of the medium in which the light variable loop is disposed. The light detector detects the light advancing thereto to produce a signal representative of the medium or the concentration of the medium in which the light variable loop is disposed.