so as you all know a ballast usually has a plug option of 120v or 240v. and i know the 240v option is so you are using less power or amps(i think)? anyway if that is the case then why wouldnt it just have the 240v option if it uses less amps. what is the need for both, i guess is my question...
The difference between 120 and 240 is 240 runs a 2nd hot wire.
If you were to open up a 120 plug in there would be 3 wires: hot, neutral, and ground
open a 240 box and there would be: hot, hot, neutral, ground.
basically when you use 240 instead of 120 you are splitting the "load" across 2 wires instead of one, ie, if a 1k watt light runs at 10 amps on 120 it all goes across 1 line, on 240 it's split so its 5 amps on each hot wire.
You can run more amps per circut on 240 but it also depends on wire gauge. but given the same gauge wires you can run more on 240. if you are wired at 14ga on 120 you can run 15 amps, 12ga on 120 is 20 amps. I'm not sure what it would be on 240 but its more, not sure if its double but you get the idea