<> ... they were vegged under 6 x 23W, 1700 lumen, 6500K CFLs. they'll be flowerd under 16 x 23W, 1700 lumen, 2700K CFLs. if you are still around i will share the results. >>

What distance do you use from bulbs to plants?

<<i'm not quite sure how you calculate a 1500 lumen bulb at 2" away doubles the lumens. i'm also not sure which forums you've been browsing where people tell you to use this method or that one CFL for veg and two for flower are sufficient. stick around here long enough and you might just learn something.>>

The light intensity is a function of the square of the distance, just like gravity. So if you cut the distance by 2, you increase the intensity by 4 (2 squared).

Because this forum's text attributes don't provide for subscript and superscript characters, I can't show the formula that expresses lumens/sq. ft. with distance using just text. So I have to show it as a graphic:

[attachment=o226671]

So if you want 2800 lumens/sq. ft from a 1560 lumen bulb, it needs to be 2.6" from plant.

Note that 30,000 lumens/sq. meter converts to 2800 lumens/sq. ft. Also note that the lumen rating on all bulbs assumes a distance of 12" from object.