I feel like I have all of this new knowledge and yet cannot lend it to making a "this is the optimum scenario for lighting a generic reef tank" statement.
You aren't alone. It's a very complicated subject and we don't have anywhere near enough information to make that sort of statement.
2) Corals like blue light in the 460nm range for photosynthesis better than most other wavelengths. If you're looking to maximize growth, focus your spectrum and maximize the intensity around this wavelength.
That's a jump I wouldn't make. There are a lot of processes to consider between the light coming from the bulb and getting usable sugar and there are trade offs and losses at each step.
First there's the production of the light at the bulb. A bluer bulb will generally put out less photons per watt of energy input than a redder bulb and as teewhy pointed out, blue bulbs often put out a lot of light that falls outside the PAR spectrum. And remember PAR matters a lot, so if you're comparing bulbs of equal wattage then the difference in PAR can have a big impact on growth even if the spectrum is good.
The next step is attenuation by the water. The red light gets dinged more here.
Then there's the absorption/ reflectance by the coral itself. The coral regulates how much and what color light even gets to the zoox and there is a huge variation in the type and amount of pigments expressed and their positions relative to the zoox. This is by far the biggest unknown quantity. The expression of these pigments is different for each individual coral and can be affected by the color and intensity of the light in ways we don't understand. Generally though, bluer light is what get's reflected or absorbed by the coral's pigment- i.e. it's not making it to the zoox.
Only after all of these other processes have had a hand in modifying the light does the activity spectrum of the zoox even come into play.
In the real-world, most people find that bluer bulbs don't give better growth, probably due in large part to the fact that they generally produce much less PAR.
3) Photosyntehtic saturation is bad. But it seems we do not have enough information to understand what approximate levels of PAR equate to photosynthesis saturation with any coral. This leads me to believe that in an effort to maximize coral growth, we could/should dump as much light (intensity/high PAR) as we can onto our corals until we observe an adverse effect that is attibutable to the intensity of light on the specific coral(s) we are observing. Additionlly if we want to maximize growth, we might as well use "the good stuff" and provide light in and around the 460nm spectrum (blue lite = the good stuff) .
No, saturation is good. That means the coral is at its maximum rate of photosynthesis and adding more light won't produce more food for the coral.
Exceeding saturation is bad. We should NOT be dumping as much light on corals as possible because many of them would be past saturation and unless the damage is severe it might now always be apparent.
Recently there has been a trend among reefers, mainly among "SPS" keepers with high lighting to reduce their photoperiods. They had good growth before but noticed that they get better growth with a shorter photoperiod. Since we know that photosynthesis isn't duration dependent, that suggests that their intensity was so high that the corals were photoinhibited and they were getting damage accumulating throughout the day. It was minor enough that it could be repaired at night so there was no apparent damage, but the excess energy required to deal with the damage was slowing growth- which only became apparent when they reduced the damage being done.
However as there is a variation in the effectiveness of the absorbtion of the photons (see the graph I linked) it is the case that if I use just photons at 550 nm wavelengh then it is less usable than an equal stream of photons of 450nm. Thus it should be weighted and count for less , and this is what I thougt PAR referred to. Is there an accepted terminology for this?
This is basically what is measured by PUR. While PUR readings are nice, it's very rarely used in practice. Actually making the measurements is complicated and takes specialized equipment, and generally it's just unnecessary. Usually PAR is good enough, and it's very easy to measure which is why it's much more widely used.
