OK! So we have agreement. The situation described above is annoying. Now how do we most effectively solve this conundrum?
1. Movie theater policy restricting silent cell phone use to below waist level, for no longer than three seconds, with no two consecutive persons using simultaneously, and with each person allowed two uses maximum per screening.
2. Movie theater policy restricting all cell phone use, period.
I know you're being totally discreet and quick and how could you possibly be bothering anyone but that's actually somewhat beside the point.
You have curious perceptions of luminance. To wit, movie screens are actually not particularly bright, considering they take up an entire wall and noticeably illuminate maybe the first two rows of the theater.