Light Closeness for Seedlings

Hi, What is the optimum distance i should have my 400W MH from my seedlings to keep from stretching, and maximize growth?? your help is appreciated, thank you.

pretty far until the reach a few nodes, 15-20" IMO

They don't need intense light at that stage. Once they have a few sets of leaves you'll want to harden them off. I usually start at 36" and work my way down over the course of a couple days. With a 400w you can get pretty close 6-12 inches without air cooling and 2-6" with cooling.