GRRRrrr! BF just lost my posting! Here goes reconstructing ...

I'm running a Luxos B with a SON hub. When I used Soubitez lately it was the old Schwinn one on my Trek, and a stand-alone Soubitez on my former Woodrup touring bike, with a B&M Oval lamp and a 4D fender taillight.

I'd agree with Jim that there is a pulse-width modulator in the headlamp, at least in the Luxos. That light gradually brightens the beam as night falls, phasing out of DRL mode into full night headlamp mode. I don't think it would be needed to control light dimming when the bike slows down, since the LEDS will naturally dim a bit when the voltage drops below a threshold. I also would not be surprised if there is a micro controller, since at least the Luxos seem to have a lot of logical functions built in.