250w in an air cooled reflector? They even make air cooled reflectors for 250w? Moondance is exactly right. Keep an eye on them, if you see excessive stretching even in seedling stage, lower the night a little, as well as still using hand test. If it is too close, you could also see some drying of leaves as the heat lowers the humidity. Ive had mine stretch trying to get to the light and the young stem cant support the crown and plant falls over. Basically, you'll have to experiment, just keep a close eye on them. If trying something new, don't do it before you have to leave to work for 9 hours, instead to it when you'll be around and can look in every 2-3 hours or so. Have fun