250watt how far from seedlings??

hi, just got my 250 watt hps and was just wondering how far to put it off my seedlings (week old)

If u have a fan right on top of light 12 inches if not I wouldn't go any closer to the seeds then 16 inches

I start my seedling sprouts under 500 watts and I start them around 2 feet away. I have air cooled hoods. So if you have air cooled hood id probably go for around 12-18 inches.