an optical couplers and optical coupling system for coupling a source of non - coherent light to a light distribution harness , wherein the couplers are polygonal in cross section to increase light mixing , and the coupler has inlet and outlet arms , and an intermediate bend region configured to achieve compactness and minimal light loss through the bend region . in one embodiment , the bend region is an integral part of the coupler , with the inlet arm having a different cross - sectional dimension from the outlet art in such manner that substantially all light directed from the inlet portion to the bend portion reaches the outlet arm portion , and light rays parallel to the inlet axis are reflected in the bend portion to be directed substantially parallel to the outlet axis . in a second embodiment , the bend region comprises a prism having a pair of parallel spaced surfaces , and inlet , outlet , and third surfaces that are non - parallel to the spaced surfaces . the inlet arm projects from the inlet surface , and the outlet arm projects from the outlet surface . one of the inlet and outlet surfaces forms a first interface with a first material having an index of refraction different from that of the prism , so that light rays within the prism totally internally reflect from the first interface .