Quote Originally Posted by Roughrider
watts are a very, very poor way of judging efficiency of lights for grow purposes. Watts are not a good way of judging how much light you are producing.
I never said it was the best way to measure how much light you HAVE.
As I said, it's just a quick and easy ballpark estimate.
You don't want <50w/sq.Ft.
If you have >50W/sq.Ft. of CFL or HID, you are in the ballpark where it is possible to grow cannabis.
Many (most?) CFL bulbs do not even put the lumen output on the package, making it quite hard to use lumens as a measurement.