Measure the voltage at the LED. Testing a new flat of 16 LS LED's here, I see a variation in voltage of 2.98 to 3.25volts with the supply set at 350mA. Since I only sampled 16, the LED you have may actually require more voltage than that to get up to 350mA.
When you first get your LED, spec it at a couple of voltages. If it consumes more than that in the future (at the same temp) then it might have been damaged in the process of your experimenting.
A good sign of damage (trust me, it is very easy to damage these, I have ruined about 3-4 so far), is that the tint becomes more yellowish or the current consumption goes up for a certain voltage/temp. I haven't smoked any so far that they don't light up at all, but several have become less efficient.
These large LEDs vary alot. It's current that counts. Just sticking one across a battery and resistor will not always draw the same amount of current from LED to LED.
Using a current regulated supply will provide better results for your flashlight. Otherwise you will need to tune the resistor for each LED you use.
Also, we sell these LEDs "AS IS" since we have no control over what people do with them once they leave here. They are very easy to damage! Experimenting with these LEDs is not a good newbie project!
Just in case people are wondering, I am talking about the LS LED here and not the Arc-LS flashlight (which is still in development).
Hopefully this simplifies the mystery for some.
Peter Gransee