Abstract: An illuminating device which employs prisms to concentrate light onto an operating area or field.The prisms are formed by an assembly of straight prism-segments which are combined into radial sectors the angular extent of which is such that the beams issuing from the source are reflected onto the field to form an area of approximately the same width as the field. Each sector thus illuminates the whole of the field, resulting in a great uniformity of illumination.Applicable to the illumination of operating tables and in general to the illumination of cavities and their walls.