I have a theory about the odd cal-mag deficiency burn condition to which LED grows seem susceptible. It always looked to me like the patterns were most pronounced where there was intervening foliage to create an outline. There is a phenomenon called edge-diffraction which acts like a prism to produce a diffraction spectrum. Led grow lights are not a full spectrum point source. They are a specific set of a discrete spectra produced by discrete sources. Now, even when this reintegrates it does not equal a full natural spectrum since it is by design a PAR spectrum. But more importantly, over smaller distances, spectral re-integration will be incomplete, so there will be areas of banding with a wide variety of different types of sub-spectra. Obviously some of these sub-spectra alter the nutrient uptake process - this is KJC's hypothesis. I agree, and the physical mechanism triggering this effect appears to be made worse as the diffraction effects of the leaves exaggerate the problem.
At about 18 inches I can just see a pattern of faint dots which suggest an overlay pattern of the intervening foliage....
