I think you can only overdrive with electronic ballasts. The standard or tar ballasts are not overdriveable. I don't know the technical details of how's and why's though. Just going on what I've read somewhere.
Just wanted to add, when they say WH7 or WH9, they mean Workhorse electronic ballasts put out by Fulham. The guys out in BC are (I think) getting theirs from Allbrite. But the
Fulham site shows that
Litemor is also a distributor. Although the address shown on the Fulham site is an Ontario store, we have a Litemor in Calgary and so it seems plausible to me if one franchise in the chain carries them, then so will another. These ballasts are cool little toys, electronic ballasts capable of many different configurations (PC, VHO, NO, PC, or overdriven NO), and cheap. The WH7 is capable of, um ... don't quote me I might get this wrong, 220W output (so two 4' VHO [2x110W] for example) and costs about $50-$60. Compare that to an Icecap 430 which also is capable of running 220W output which costs more like $200. I know Coralife and I think some other VHO ballasts are also available but I think they're in the $100-$150 range and plus they're only VHO I think (ie., not capable of running other different configurations, eg. PC) so when you look at that it's pretty evident why these WH ballasts are popular.
I apologize if everyone already knows all this, just wanted to chime in with my own two pennies worth...