Quote Originally Posted by psteve
If it never gets bigger than 16 inches!
You need AT LEAST 50W per square foot of floor space. Even 100W per square foot is still not that much. Especially with CFL's.
Well, what you want to look at is lumens per square foot...different lights are more or less efficient in producing lumens, so watts (which is a measure of energy used, not light produced) isn't the way to go.

Quick 'n ' dirty chart--

Under 2,000 lumens sq. ft.--Nothing
2,000-3,000 lumens sq. ft.--Next to nothing
3,000-4,000 lumens sq. ft.--Marginal to okay grow
4,000-5,000 lumens sq. ft.--Okay to good grow
5,000 lumens+ sq. ft.--Very good/optimal grow

This is why a 400w HPS is good enough to take care of a 3' x 3' area...that's around 50,000 lumens in 9 sq. ft. 5,100 lumens sq. ft. I've used a 250w bulb in a 27? x 27? area...27,000 lumens in 5 sq. ft. Works fine. HPS lights tend to be 25-70% more efficient than CFLs, which is another good example of why you should look at lumens, not watts.

60 watts of CFL is going to give you ~ 4000 to 4200 lumens. You're in the okay area for one sq. ft. 75 to 80 watts puts that up to 5,100 to 5,600 lumens. It's always hard to tell if people are growing giants, but I have fit 4 good sized (around 3') plants into a 5 sq. ft. area. I figure a decent plant with a decent yield will take up 1.25 sq. ft. 5600 lumens is about 4500 lumens/sq. ft. for a plant that size... not optimal, but will do okay. I've seen what $7 worth of Wal-Mart Warm White bulbs can do for one plant, and it's good??that's 92 watts and 6600 lumens.

If you're doing massive LST, you may get a plant that's 16? tall and 16? in diameter. In my experience, with normal LST or topping, a plant is more like at least twice as tall as it is wide. So a 3 foot tall plant is more like 12?-16? in diameter...and a grow area that's 12 to 16 inches square is between 1 and 1.7 sq. ft. That's 5000 to 8500 lumens to get into the optimal area. So 75 watts is a little short...it's on the low end of that. 90 would probably be fine. But it's still about lumens per sq. ft. CFLs are pretty consistent in giving about 70 lumens per watt, so 70 watts per sq. ft. of grow area will be fine.
Roughrider Reviewed by Roughrider on . 3 weeks, 1x60watts cfl, opinions pls! Here we go, my first plant http://img507.imageshack.us/img507/188/imagen1473qx2.jpg http://img523.imageshack.us/img523/6948/imagen1474zh3.jpg http://img172.imageshack.us/img172/2008/imagen1475yn6.jpg http://img214.imageshack.us/img214/6114/imagen1476vx3.jpg Rating: 5