What would be the absolute max you can flower under 1 600 watt HPS? I have someone who says they want 10-15, I told them 10 would be pushing it, just wanting to make sure on this one as I have no experience with 600.
Since plants come in all shapes & sizes and the light can be used to cover more or less ideally sized areas, you can't really say what a given lamp will support in terms of number of plants. A 600w supports maximum growth in a roughly 3.5' square floor area, which will fit 3x3 plants in 5gal buckets. You can take it a bit further with a light mover or daily rotations but would get more stretching and a lower average potency.
Could always ScrOG to get more budsites under that light....10-15 is not unheard of for a 600w light.
Hey guys, I currently have 3 BC females growing in a 3x3 area and they are coming out a treat! Give more light to less plants and you will see the difference in quality that adding supplemental light can give.