How many lights do I need?

How many lights do I need for 18 babies. I have been using 3x 1000 HPS for 18 girls. I wondering if I should get one more to increase my yield. Or is 3 enough. What do you guys thinks?

1 1000 for each 6 girls sounds good enough.But if you can add the next 1 and money is not a problem it will definately increase yeild.

What style of growing are you using? seed or clone? how long do you veg for? some people will put less plants under each light and veg them for much longer, others will put many more under each light and have significantly shorter veg time. hope this helps