See it in action here in comparison to other flashlights:
And the morse function:
The light can be seen from a very wide area and is great for morsing through the night.
A monster flashlight containing a 100W 8500Lm led with big heatsinks and batteries.
With morse function to tell the night goodbye.
I wondered about the arduino, because for dimming I would just use a pot and adjust the constant current. It is not that great to PWM the LED current itself. This gives flicker (depending on frequency) and reduces efficiency. The efficiency of LEDs goes down with higher current. Therefore the overall efficiency goes down if you use high current pulses with pauses in between for dimming. It's true, that it is often done this way, but just out of convenience. You have a real switch mode converter, so you can drive it with DC.