Whatever you find uncomfortable your plants do too.
Place your hand underneath your light and see how close you can have your hand before it becomes too warm. A little bit below this too warm zone is where your plants can be to get the most light without having to worry about heat stress. A gentle fan blowing above the seeds but not onto them can disperse some of the heat and as your seedlings grow a gentle breeze will also help strengthen them up a fair bit.
You can do HPS the whole grow in case you were wondering. A lot of people will tell you MH is better and it's only a little true. With it's high lumen output HPS is perfectly fine for vegetating and many growers go straight HPS the whole grow. Of course there is no downside to full spectrum lighting but use what you got man, looks like you're off on your way to buds.