(Context: the original comment mentioned dark fiber, but I changed it to be more precise to avoid exactly this confusion.) Dark fiber is a bit of a misnomer and term of art, IIUC. The way I've had it explained to me, dark fiber is not necessarily dark. It's just not on the public internet. When you lease dark fiber, you presumably do so to put your own signal on it, making it no longer dark. But folks still call it "leasing dark fiber" and still refer to the fiber, once lit, as "dark fiber." I'm not a networking expert so someone please correct me if I'm wrong.