Matt,

I'd like to take a course from Sanjay. As you point out, he's where a lot of this knowledge surfaced originally.

Yes, lumens as a measure are skewed toward "brightness" perceptible to the human eye. And you're right; PAR is the right measure to use. As soon as I can get published PAR values across all the MH bulb options (we may already be there; it's been a couple years since I checked), I'll switch to that measure of evaluating lighting schemes.

The problem I still have in my mind is adjusting intensity at the surface over reefs (it doesn't matter whether you're measuring lumens or PAR) to intensity from a MH bulb envelope, and tracking the decrease in light as you move down through the water (something like an intensity reduction per foot in the ocean vs. per inch in our tanks). The formula is somewhere in one of these articles, but the main idea is that light intensity decreases with the square of the distance, according to the original intensity. You can see immediately that a couple extra inches' depth is really going to matter in our tanks, where a couple feet's depth doesn't make much difference in the ocean. Anyone thought about that enough to teach us all something on this subject?

Dean