I consider the Solarforce a bit large for helmet light. I recommend the Uniquefire 2100 or Yezl (something) or Shiningbeam S-Mini (XP-G version will have a bit more throw than XM-L version). These lights are all under 5" in length and 1" diameter and they have a straight body, ie no large head. Solarforce is a good choice for lights; they are better quality than the Junkfire (as I call them) random lights on the HongKong web sites.