A light-beam-scanning system includes two counter-rotating prism wheels. Each prism wheel has a set of prisms at its periphery, selected so that prisms of equal half-angle deflections are sequentially aligned. A light transceiver structure directs a light beam parallel to the rotational axes of the prism wheels and at a distance from the rotational axes so that the light beam passes through the aligned prisms. A prism-wheel drive is operable to drive the prism wheels in opposite rotational directions.