Well part of this is the loose term of "UV".
another part is the different divisions in UV
Some UV-a is used or useable in photosynthesis directly.
Some UV "irritates" the corals enough to produce nice colorful pigments
Some UV "may" help health by irritating bacteria and other pests.
I've yet to find any real documented proof that UV does anything more than the above.
Blue on a par to par basis can substitute for many of the "UV" effects.
From a terrestrial plant perspective, not that it means much..
Light signaling and plant responses to blue and UV radiations—Perspectives for applications in horticulture
Ultra-violet (UV) and blue radiations are perceived by plants through several photoreceptors. They regulate a large range of processes throughout plan…www.sciencedirect.com
This what you said here:
Some UV-a is used or useable in photosynthesis directly.
Some UV "irritates" the corals enough to produce nice colorful pigments
Some UV "may" help health by irritating bacteria and other pests.
That *sounds* right to me, it seems plausible... I just want to see how it is actually known with science.
Also, I think there is a lot of confusion about the spectral distribution charts they use to show the spectrum... those are all ratios, not absolute values. When people say the SKY has no UV, that is incorrect. EDIT: assuming their (BRS) equipment is working and accurate and they are presenting the data correctly.