Abstract: A device for operating frusto-conical optical concentrators made of a refringent material of refractive index n, the major base of which is in the vicinity of a source S, said device comprising, at the upper portion of a frustum of a cone, a frusto-conical reflector surrounding said frustum over a given height along the frustum axis of symmetry, the inner surface of said frusto-conical reflector being parallel to the frustum lateral surface and located at a small distance therefrom, and said given height being at least equal to the ordinate of a point A as measured along the frustum axis of symmetry from the apex of said frustum, point A being the point at which the ray emitted by source S which is the most inclined with respect to the frustum axis of symmetry, undergoes its first reflection on the frustum surface, at an angle to the normal to the frusto-conical lateral surface at point A, said angle being smaller than the angle of total reflection.