If you were to grow 75 plants from seed to seedling (2-3 weeks) how many watts of HPS light would you need? Would 2 400 watt HPS lights be enough seeing as they are only going to be getting 5-10" tall?
5-10 is not a seedling. seedlings need no more than a fluro. After a couple weeks when they are ready, then one 400 may work depending on how you pack them in. 2 may be better. I just judge my plants when they can go to HID. I believe the rule of thumb is when they have their 2nd set of leaves