250 watt HQI ballast.

[Delphinus]

I'm not sure I get it. Does the pfc. (or whatever) value have any bearing?

Ok. Let me try it this way... So if I was going to install a subpanel in a tank room, I'd use a 220V feed for that and have separate breakers for each 110V circuit. If I had that, then conceivably I might just leave a 220 circuit for the ballasts and any pumps I had that might run off 220.

But assuming that I don't currently have the subpanel, and don't have any equipment that runs off 220, I don't know that I see a benefit to the effort of installing one 220V circuit. The lights aren't going to burn any brighter, the ballasts aren't going to run any less hot, the watts consumed aren't going to be any less. Essentially, it comes down to "what plug do I want to use?"

The "double your load" thing really only strikes me as a benefit if I was on the borderline of overloading one circuit. In which case, I might just string myself some extra circuits anyways and just do a careful load balance to begin with?