An optical system (20) for efficiently collimating an elliptical light beam includes a light source (21), a collimator (22), and at least one prism (23,24). The light source is adapted for providing an elliptical light beam defining different diverging angles in different directions, wherein any cross-section of the elliptical light beam emitted from the light source defines a long axis and a short axis which are perpendicular to each other. The at least one prism is used for reconfiguring the elliptical light beam, thus obtaining a parallel round light beam having equivalent short axis and long axis.