Vaughn, you may recall the spherical LiCor meter probe I was talking about, take a look at thise link and you see why and how they decided this made more sense.

Inverse Square Law for Light
I heard some reef folks discussing this back in the early 1990's.
So I've had this in my head for many years.

However, we can take this a few steps farther:

Facts of Light – Part 2: Photons by Sanjay Joshi - Reefkeeping.com

We do not have tanks that are over more than 1 meter in general, there are cases, but very few and then not ever more than 2 meters.

So we can then discuss how the PAR is distributed with the spectral plots of PPFD.

He has a good set of useful readings:

Sanjay's Reef Lighting Info Pages

Still, this measurement does not tell you what the light actually is at the coral, or at the plant top, near the edge of the foreground plants on one side of your tank, within the plant groups, nor says anything about how the light changes through time as the plants grow.

Some plants of mine grow 4cm to 12cm a week.
They change their light status every day and pretty much each hour in many cases!!!

So that can change the CO2, and nutrient demand.
So maintaining lower light and pruning often will lead to more stability.

However, if you can handle high light systems, then you can handle the slower easier to deal with lower light systems as well.



Regards,
Tom Barr