That 20mm figure means it catches a finger reaching into the hazard zone — finger-protection class per IEC 61496-1. The 84 beams at a 15mm pitch cover a 1265mm protective height, so it guards a vertical opening about the height of a typical machine access point. Operating range spans 0.2m to 9.0m, giving you flexibility to set it back from the danger area.
Safety light curtains like this one guard point-of-operation hazards on assembly stations, presses, packaging machines, and robotic cells. The blanking and muting functions let it ignore fixed obstructions (like a fixture) and automatically bypass during a material pass cycle — handy on a conveyor-fed line.