Buy two of these:
http://www.keygos.com/product_info.p...k8fvnjkt7527u4
The head strap can be used on a helmet by putting the straps through the holes. You'll have lots of flexibility since all the parts are interchangeable and extra batteries. Everything in the picture will come in the package (I've been asked this once since it does seem like a lot). I've thought about buying another myself but I just don't see the need for a helmet light in brightly lit NYC.