In my opinion, it may be a little much for brand new seedlings to have it so close - I move my light about 3 or 4 feet away from brand new ones for a few days and gradually get closer after that. You might want to get a couple of CFL while you're at HD...few days under CFLs (close - inches from seedlings) and they'll be much more prepared for the intensity and heat of the 400w.

Good luck & happy growing