After the roots develop and get stronger (usually about 2 weeks) there is no real reason not to put them under 400w. And depending on heat and ventilation you can put it pretty close as well. I use a 400w HID with cool tube and fan. I keep my seedlings about 12" away from them.
What you may want to consider is...you have quite a few plants there...maybe too many for that much HID. How big is your grow space?