in a particular direction with respect to said table moreover it is also possible to adjust the angle of incidence of the light line 36 by rotating said header 31 about an axis parallel to the running plane and perpendicular to the run direction finally in order to take account of the various mechanical tolerances it is also possible to modify the inclination of the header 31 by making it pivot about an axis parallel to the run direction in this way it is possible to move one side end of the header closer while moving the opposite end of said header away from the cloth each individual header 31 see fig3 is composed of a light source 40 which contains in a housing 41 a halogen lamp having a typical power of one hundred and fifty watts and a fan type cooling means 43 this housing is connected to a bundle 45 of optical fibers in order to avoid degradation on account of the light power involved of the cement forming the end 50 of the bundle 45 a heat absorbing filter 44 is inserted between the lamp 42 and said bundle the bundle comprises several tens of thousands of parallel optical fibers combined together in a concentrated manner in the form of a cylinder in the distal region connected to the light source 40 as has been shown one of the main characteristics of the invention is the formation of a line 36 of light by means of the light header 31 for this purpose the terminal end of the bundle is opened out and moved apart so as to form as straight an assembly as possible the thousands of optical fibers having a typical.