Light in the root zone is supposed to impede root development slightly, but not completely. Cuttings in water will root faster if they have no light shining on their root zones than cuttings that do recieve light on their root zones.
I've rooted Neps in LFS mixes, and rooted one troublesome Agri-starts Rafflesiana in water. It was a last ditch effort; after a while of no rooting with the brown stem buried in an LFS mix, and then (a few months later) sitting in water, I cut off the brown stem, sliced the bottom of the green stem, dusted it with a little Rootone, and set it on my windowsill. It grew roots to about an inch long, then I potted it up without trouble. I would still suggest LFS mixes over water, though. I believe that if I had stuck it in an LFS mix after cutting tyhe brown stem off, it would have rooted just as well.