The 1100 is considered directional in that it appears brightest when viewed from certain angles; straight from the rear and straight from the sides. The 500, for instance, is not as bright, but it spreads it's light over a wider area; the light appears to not be less bright when viewed from a greater angle. The 500 is also much lighter weight and a CPSC certified reflector.

I suggest the 1100 for your seatpost and a 500 for what I think you might be looking for in a helmet light.