Research developed a laser bridge based technique for online testing of glass or carbon filament breaks in yarns, yarn sheets, and textile fabrics during manufacturing processes. The technique facilitates the evaluation and optimization of materials, processes, operations, and machine components. System capabilities include detection of the passage of a single broken filament through the light bridge. The sensitive detectors evaluate filaments of less than 5 microns at speeds of up to 1,000 meters per minute. A central computer controls the system through a Microsoft Windows operated program and records filament damage, yarn tension, test material movement dimensions, and test time. 7 refs.