witha 400 hps, u can cover a area of 3ft by 3ft so 9 plants max..I think for my next grow im gonna get a 400 watt hps I was looking around and I could get a basic one for around 200. If i had a 400 watt light how many plants would I be able to put under it? I think it might be easier to have 5 huge plants though, so if i had 4-5 plants how tall would i be able to get them?