It's pretty bright but I'll do some objective comparisons to a 150W condenser head this evening and post the results here.
Originally Posted by Bob Carnie
The app just sends a burst of data at the beginning of an exposure to a microcomputer in the lamp head. The microcomputer does the actual timing. The phone can actually be shut down during an exposure and the timing will still proceed correctly.
Originally Posted by MartinP
The light from the phone set at lowest brightness (still quite visible in the darkroom) seems to be paper safe at a distance of 12 inches or so but I haven't rigorously tested it. The colors for the buttons were chosen so as to have minimal effect on photographic paper. However if you wanted to be absolutely sure, your options are to sleep the phone, cover the display with a red gel (like from an office supply store), or simply flip the phone over on it's face.
Thanks everyone for their comments.