When to increase light intensity for my autos?

there are good suggestions out there, but always remember to trust what you see above all else in this one context. Use the resulting internode length (stem between 2 growth nodes is an "internode"). If nodes are too tight, you need less light. if internodes are too long, you need more light. the suggestions get you in the ballpark. some trial and error will be required on your part. Take notes about power and heigth from canopy. Environmental factors influce this too, so you may have different needs based on different seasons, for example. The more tightly controlled the environment is, the more consistent these things will be over time with fewer adustments needed for any 1 grow cycle. its a quasi-QB if i recall (shape/frame of light)? So 18" is a good distance. Further choose by coverage -- this is geometry at work. you want to cover your edges and corners of grow area as well as you can without sacrificing too much in central areas. Further distance gives more even coverage from center to edge -- higher is not always better, of course. higher from canopy may require more power, but also will give better penetration (relates to inverse square law and how light spreads out over distance.). So a bit wasteful but possibly make that up with more substantive lower buds than you would from a closer distance. 1/d^2 -- where d is original distance from light. think of this as "1" increment. so a single point of light that provides enough at 12" vs one point of light that does the same from 24" but covers a larger area (more power needed)... 12" deep into first example is 1/4th or 25% the amount of light vs 44.4% (1/1.5^2*100). You can see how inverse square law is relevant to making a better decision. this example is watered down. the reality i smore complicated because we have hundreds if not thousands of points of light (each LED diodes). the overlap of individual points of light will mitigate this effect in central areas much better than along edges. If you go test this with a quantum board, you could gugesstimate some factors to use instead of 1/d^2. if lux is 40% less at twice the disctance, you can see how the overlap of diodes greatly reduces this effect but it is still a huge factor. (just guess... i bet its 40-50% though instead of 1/4th with a smallish quantum board and mesuring anywhere near middle at the 2 different distances. so if money is no concern, be wasteful with higher from canopy distance and a bit more power... common sense = at some point raising the light doesn't help much more than previous distance and only lowers overall DLI given to plants. this is obviously "too far" relative to equipment used. 24" is about as far away as you'd want to go with a QB, then adjust power to get proper internode lengths and overall growth. Early on there is no need. the plants are short. The taller the plants are, liek in flower, the more useful this is. You still want to make sure you are approaching 35-40 DLI applied to entire canopy as a whole... i wouldn't sacrifice overall energy provided for a small gain on edges, for example. each context has its own optimal answer. cause and effect can lead you where you want.