smoke24answered grow question 4 years ago Truthfully, you want as close as the plants can handle. Different strains have different light needs, the best bet is to follow the manual that came with the light. seedling (30in), veg (18-24in), flower (12-18in), and then fine tune within those ranges based on how the plant reacts to the light levels. Leaf serations curling up and tacoing are signs of too much light/heat, excessive stretching and large internodal spacing would be signs of not enough light. Hope this helps. Happy growing.