here try this
Example of Estimating Number of CFLs Needed For Your Grow Space:
1.
Multiple width x length of your grow space to determine the sq feet.
Let’s say your grow space is 2’ x 2’ = 4 sq feet

2.
Multiple the sq feet of your space by 4,000 lumens to determine the total lumens needed for this space.
So 4 sq feet x 4,000 lumens/sq feet = 16,000 total lumens for that space

3.
Divide this number by the lumens produced by each bulb
If you’re getting 42W CFLs which are rated at 2,650 lumens apiece, that would be 16,000/2,650 = ~6

4.
This number is the minimum number of CFLs needed for your space
That means in this case you’d start with 6 (or more) 42W CFLs