An optical waveguide includes a body of optically transmissive material defined by outer edges and having a width substantially greater than an overall thickness thereof. The body of optically transmissive material includes a first side and a second side opposite the first side. An interior coupling cavity is defined by a surface intersecting the second side and extends from the second side toward the first side. The interior coupling cavity is disposed remote from edges of the body and is configured to receive an LED element. The body of optically transmissive material further includes a first array of light mixing cavities surrounding the interior coupling cavity and an extraction feature disposed on one of the first and second sides. The light extraction feature at least partially surrounds the interior coupling cavity.