An optical element for a light based touch surface including a concatenated plurality of segments, wherein each segment is paired with a respective light emitter, each segment including an undulating series of pairs of reflective or refractive facets, wherein a first facet in each pair is oriented so as to collimate light emitted from a first light emitter associated with the segment and a second facet in each pair is oriented so as to collimate light emitted from a second light emitter associated with the segment, and wherein the first light emitter associated with the segment is the light emitter paired with the segment and the second light emitter associated with the segment is the light emitter paired with a neighboring segment.