I read somewhere..i think jorge's grow basics book that an hid light should be kept 3-4 feet away from seedlings for good growth.it sounds a bit far and was wondering what the experienced growers on this site did.i have a 400 watt with radiant hood and kept it about a foot away from seedlings but have been having slow growth problems. also for the first 2 weeks of growth from seed and a normal 75 temp with 50%humidity how often should seedlings be sprayed.also is spraying a good idea throughout the seedling stage until the plant starts taking off.im def not trying to overwater or water to often and figured its pretty impossible if you only spray a couple times a day.
id keep the light atleast 2 feet away. depending on how much heat its putting out under it, feet it with your hand, 12" us usually pretty hot, but might be ok for a 4 week old plant.
You can use a HID for your seedlings just keep it about 36'' away or 3 ft. and keep them on the outside perimeter of the light for the first week to two. Nothing wrong with giving your seedlings a mist either, just don't overwater them. Best of luck!