and I mean dim like a *little* bit... not much at all
is that okay?
i would imagine so. mine does that if i apply the front brake. it isnt enought to notice unless i am on a dark road at night.
why?
The brightness of the headlight is dependant upon how much voltage the stator is putting out. At higher rpms the stator is creating more current, and when you brake you go to lower rpms and the current is reduced.
by dimming do you mean that the light it's self is not as bright but it still goes as far, or it might be that the front suspention is compressing enough that the angle of the headlight is steaper and therefore not projecting light as far.
Also your electrics only produce a certain amount of currant.
When you break your break lights draw power and this leaves less power for the headlight, so your headlight dims.
Add to this what Dom said about the power from the Stator being dependant on RPMs and you can see why breaking does this.
I've noticed in traffic at low RPMs that my headlight dimms in time to my indicator lights.