This might be a silly question, but what about pocket lint? I received a non-brand LED flashlight as a gift a year ago and it is/was really bright, but I've found that the little depression in front of the LED is almost always filled with fuzz. I always remember to blow that out before using it, but there seems to be a constant layer that needs a damp paper towel to remove. It's just one thing that's a bit annoying.

Why not just build them with covers?