fig1 for the articulation of the ribs 5 in the bearing body 7 instead of the radial slots it is also possible to provide bores arranged in a circle on or in the bearing body especially through bores in the bearing body 7 that are elongate in the radial direction which bores provide a connection between the side of the bearing body 7 facing the canopy 3 of the reflector 1 and the side of the bearing body 7 remote from or opposite the canopy 3 of the reflector 1 in principle however there are also other possible ways of effecting articulation of the ribs 5 on the bearing body 7 in such a way that the ribs 5 are able to pivot into their open position and vice versa in the embodiment of the invention shown in fig1 a force effect is exerted on the projecting portions 9 of the ribs 5 by a pressure plate and especially by a pressure ring 11 which in this case by way of example has substantially the same outer diameter as the bearing body 7 the pressure ring 11 is arranged substantially parallel to the bearing body 7 more specifically on the side of the bearing body 7 opposite the canopy 3 furthermore the pressure ring 11 is joined to the bearing body 7 by way of a plurality of guide bolts 13 the bearing body 7 and the pressure ring 11 are movable relative to one another so that the spacing between them can therefore be altered displacement of the pressure ring 11 can.