Hundreds of watts of CFL SOG in cardboard boxes in an attic (Alaskan Ice).

That plant is over a month old? Looks like mine at 2 weeks.. What are you using to fertilize? Looks like some N deficiency which is why it's consuming the lower foliage. Are you PH balancing your water?

Looks to me that your nutes are not tuned correctly. You should test the ph of the soil to be safe. My first plant ever had the same problem with the lower leaves dying at around week 3 of veg. However in my case, I had not yet applied any ferts. After a few low dose nute feedings for veg growth she recovered, but the lower leaves didn't of course.

Good Luck