I'm curious.
Is this for Offroad/Enduro purposes, or for road use?
If for offroad, why not rather use a helmet mounted light? Works a lot better than the headlight on the bike coz it points where you look.
I use:
http://usd.knog.com.au/crystalnews/qudosaction/
Mounts on a gopro mount so you can stick them anywhere. It's nice and vertical so ideal on the side of the helmet, just behind the eyes opening.