  The Hyper-Kamiokande neutrino detector is set to begin construction in 2020,
succeeding Super-Kamiokande as the world's largest water Cerenkov detector.
Research and development are well underway for an integrated light injection
system for Hyper-Kamiokande which will provide in-situ monitoring of
photo-sensor responses and water transparency. In summer 2018, optical hardware
forming an iteration of this system was installed in Super-Kamiokande. We
present details of the narrow-beam diffuser hardware and testing procedures, in
addition to a brief summary of the installed light injection system.
