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my advice. If you are deciding between two lights say 250w and 400w go with the bigger (As long as you can afford) b/c more light more buds and if you ever decide to grow more you'll have the capacity.
thats a good point. you also want to take into consideration, 'how many females are you going to be left with?' unless you are going with feminized seeds, i wouldnt expect all 4 to go the distance. either or will be fine if you have the money, but if you only end up with 2 or even 1 female, 400w would be alot of energy to spend on just 1 plant. its all about the benjamins
id say get a 400 hps... and use your mh for clones/veg. and make a harvest every 60 days..... dont worry on the 400 hps compared to mh (the watt to lumen ratio is different) because hps still has the advantage with lumen and spectrum output..