This procedure describes light launch conditions to the test fiber for the purpose of achieving a uniform overfilled launch with a laser diode or other light sources. While FOTP-54 can be used to establish overfilled launching conditions for the measurement of various fiber parameters@ it is principally used in conjunction with FOTP-30 or FOTP-51 for measuring information carrying capacity. Light launch conditions are established through the use of a mode scrambler. The mode scrambler is positioned between the light source and test fiber to produce a radiation distribution overfilling the test fiber core and numerical aperture@ irrespective of the spatial radiation properties of the light source. For many mode scrambler designs@ however@ the launching conditions produced depend on t h e source/mode scrambler alignment and the interaction with any intermediary optics such as connectors or optical imaging systems. If the source or any component in the optical system is changed@ the qualification tests must be repeated. When applied to information transmission capacity measurements@ the overfilled launch gives good measurement reproducibility; it is not intended to necessarily give the best bandwidth prediction for concatenated lengths. Also@ a particular light source/mode scrambler combination may be satisfactory for one size core diameter and numerical aperture test fiber@ but not for another.