What is "120AC/170RMS"? In the US you have 120VAC RMS. And there are 50 series sets of 2 in parallel? (Or 2 sets of 50 in series in parallel but that results in the same.) That is an odd arrangement for 240V countries which in which they probably just sell 100 in series which results in the same voltage. That would make them 2,4V each. Just don't go over that, done 
Messing around with "looks to be the same brightness" is just to vague. Or eyes are terrible at spotting differences like that. And the voltage they directly blow at and the voltage they might blow at after some time are completely different
Doug101:
Wall wart is not a transformer, not heavy enough, there's a chip in there.
But did you measure it?
Doug101:
I'm wondering if maybe I should add a resistor in series to drop the voltage a bit?
Might be an option but you need to measure the current for that as well.
Doug101:
Or a zener?
And leave to rest of the voltage where?
Doug101:
Or maybe switch to 12v, and use a bcuk voltage reducer. And that will give me 12 to power the Arduino.
Why 12V? The Arduino is a 5V device (even less at lower speeds). Will work with 5V fine, only connect it to the 5V/Vcc pin or USB, no to Vin. Only don't simultaneously connect it to your computer (that's why doing it via the USB is a safe option).
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