Update on performance
So it's pitch dark in the house and I tried one of the units on a helmet.
The mounting wasn't quite as sturdy as I'd first thought, specially with the helmet cover removed. I want to try and find a way to maybe shim it.
So mounting issues aside, in darkness the amount of light these put out -- even on the lower settings -- is adequate once your eyes have gotten used to the dark. On the highest setting it was bright enough to see clearly down the hallway. The lowest setting provides enough illumination to see what you're doing and even to read something without adversely affecting your natural night vision too much. After a few moments of testing it, I was actually surprised how dark it was after I turned it off (from the lowest setting).