A spectacular job.
I'm also making a lightsaber with Arduino ( 80x 5mm green leds, WT5001M02-28P U-disk audio, ultrafire 3,7v 6000mAh x2 batteries)
I have seen the circuit and have a question:
The LEDs are separated by segments which are activated with Arduino through a mosfet transistor...
But... when a part of string is activated.. it's reciving 7,4V?
Is not necessary to use a regulator or resistance to prevent damage?