Abstract: A lens particularly suited to elongated grooved lens holders such as heat sinks for light emitting diodes. The lens may have a curved surface which projects light in rectangular beams and a radial flange for engaging grooves of a grooved lens holder. Curvature is that of a flattened or compressed sine wave, with less than one full wave being formed along the lens. In one aspect of the invention, the crest of the wave, which would ordinarily be domed, may be flat. The radial flange has straight sides to enable contiguity when arrayed in abutment as well as for cooperating with the grooves of the lens holder.