An ambulatory device for use in therapeutic and/or cosmetic treatment has a localised light source such as an LED (e.g. 6 19 46 119 219). Light from the source is output through an output surface which, in use, covers the area to be treated, and light is distributed over that surface by means of a diffusing member (e.g. 14 114 214) of which the output surface may form an integral part.