adrian_h:
BTW, what is the Vin for? Is it just raw power without a current limit? At least not limited to the board, but the power supply that supplies the board?
Yes, "Vin" is the input voltage as delivered from your external supply / battery.
The LEDs should be between +V and the collector, not in the emitter (which ought to go straight to Gnd.)
(Vin - V_LEDs) / ? = Amps