While dealing with a phone’s noise and brightness would certainly curtail some of the annoyance caused by cell phones in dark rooms where people are supposed to be quiet, it’s not like reducing that would remove the problem entirely.
Theaters are dark, so any light would be a problem, and certainly these devices would produce some light.
We are, of course, completely sure that this idea will go off without a hitch and nobody will have a problem with it at all.
Either that or people are already picking up their pitchforks and torches.