The SF4000 is a very intense light. Depending on plant size, I would run it at 50% and 24" for just germinated seedlings. 75% and 24" for vegging. Allow the plant to grow into the light at about 16"-18" raise it again to 24". When you flip to flower 12/12, turn your light up to 100%. Keep the 24" distance to start and again allow them to grow into the light. During flower, you can get as close as 12" but watch the plant. Not all are the same. It will tell you when it's getting too close and you might have to raise it sooner if you begin to see signs of light stress.