You'll direct drive it if the Vf of the LED is less than the voltage of the battery. It's not a recommended configuration. The up and coming Arc (LS4) should be able to take a much wider input range (2AA's to 2x123 I believe)
At the Arc-LS Instructions,you can find:
-The circuit will operate in a voltage range of about 1.4 to 3.8 volts...
Why do dot the factory recommend use batteries over about 3.2 volts?
