I would use a lot less powerful light than that for seedlings. You're going to fry them. Even if that's all you have and hang the light 5 ft away, the seedlings will stretch terribly.
I always use the old trusty hand under the light technique, but really if they're just seedlings I'd dim the ballast as much as I could and probably put it a good 3 feet or so. I use a 400w straight thru and usually just keep it 3-4 feet off my seedlings mostly just for the convenience of being able to work easier in my tent with the light higher up.
Also, that's a lot of money on electricity. Although your 600 turns down, it doesn't go down to 40w.
