you should be able to get a 250 watt lamp alot closer than 18 inches would expect you should be able to get it within 5-10 inches from the lamp to the tops of the seedlings do the hand test to help determine how far away the light should be, put a small fan on the seedling to where they are barely moving a little.
and when you transplant in a week or two plant them deep up to just below first round leaves.