Those thing have come a long way. Back in the 80's we used cyalumes attached to SCUBA regulators for night diving...bright enough to see people but not too bright.
Now days we use the super tiny "bobber lights" (1" long) taped to the bottom of disc golf discs for night golf. Those things are very bright and you can track your disc through the air and on the ground, easily. I've hung full sized ones from the tops of sailboat masts and on the bows of kayaks. They are absolutely waterproof. Never used them backpacking though....there are lighter, brighter options.
My biggest hangup is they are "disposable" and create trash, so they are a last resort.