I am using the 12v 6A external power supply to power the LED. And yes, I calculated that 3A will be needed for 50 so I bought the 6A power supply. And for the base resistor, if it's 200 ohms at 5v, what would it be at the 12v??
I am only doing this with one LED so far so this is why it's confusing me why the light it dim. I could understand if my power supply wasn't strong enough for all 50 or the arduino couldn't power all them...but I've only tested this with one LED so far. The LED is not broken so it should be full strength like it is when I directly connect it to the power supply without the transistors =/
Just remembered too which could be useful. When the arduino is powered with a 9v battery the LED doesn't even turn on, but when powered through USB it's brighter, but still pretty dim. I know the USB supplies more current, but with only one LED this shouldn't make a difference =/