A beam expander (100) of the invention is a single moulded transparent plastics body having a planar light input surface (101), circular in end view, upon which input light is incident, and a tapered outer reflection surface (102) forming a frusto-conical shape. A planar light output surface (103) faces in the longitudinal or axial direction and a tapered reflection inner surface (104), in a frusto-conical shape, is formed by an on-axis recess in the moulded body. All of the surfaces have an axis on a longitudinal axis of the device, namely the optical axis. Light is directed by the inner reflection surface radially towards the outer reflection surface, where it is again reflected back to axial, but with a much longer beam diameter. The overall length (t) of the beam expander is very short.