Lamp setting viparspectra p600

if doing photoperiods, you should shoot for whatever distance works well for 66-70% and 18h per day. Otherwise, you'll be underpowered in flower phase. When you switch from 18h operation to 12h operation, you need 150% of previous power to maintain the same DLI, give or take. So, 66% becomes 100%. Distance should be about coverage - geometry. Choose a distance from canopy that properly covers the target area from wall to wall without sacrificing overall average intensity across entire canopy. A klux meter on phone can be helpful for measuring proportional intensity relative to central readings directly unde the light. it's a qb, so 16-20 inches is probably good as long as light spreads out well to entire target area. The klux meter will help you decide. their par maps are fairly useful reference too. 100w for the efficacy of that light is good for just under 3 sq ft. so 1.7' x 1.7' is a good target area. The 2x2 suggestion is a bad suggestion by vipar. It can probably do it, but DLI is going to dip into mid to upper 20s, and that's going to increase the proportion of larfy buds near edges and deeper into canopy.