An elongated lens (300) is formed with a trough (310) along the long axis on the light emitting surface of the lens. The elongated lens (300) may include a curved wall (325) about its perimeter, and a smooth transition (317) between the curved wall (325) and the trough (310). The trough (310) may include a concave shape along both the long axis and the short axis, although the radius of curvature of the concave shape may differ between the long and short axes. The eccentricity of the illumination pattern may be controlled by the size of the trough (310) and these radii of curvature.