A pal that ran a sog garden using hps did some experimenting with the lite intensity. He ran the same strain of clones in the same system for several crops. Lumens were 1-50w psq, 2-75 w psq, 3-110w psf. He said he didnt notice any difference in yield or growth beyond 50w psf, but managing the extra heat and elec usage were a chore.