I have had a couple of runs with these lights now, and it took me a bit to get used to them. At first, I was running them too close, and it actually lessened the yield. I ran the last click with them at a constant 48" above the canopy and hit huge.
What these lights do is enable you to light up a bigger square footage then a traditional HPS. On a 4' x 20' table, I would normally run 6 traditional 1000w hps lights over the table, where now I light it with 4 DE 1000w and increased in yield with lower power.
I do have 1 row of AC/DE, the Aircooled Dual Ended hoods, so 4 of them also covering a 20' x 4' table, and they hit just as hard as the non air cooled too, I was impressed. I was able to run them a little closer, about 30"-36" above the canopy, but had a little light bleaching on some of the tops. So, for a guy with height restraints and cooling issues, the AC/DE hoods worked well for me.