View Single Post
Unread 04/09/2016, 10:02 AM   #52
rfurst
Registered Member
 
Join Date: Dec 2006
Location: Danville PA 17821
Posts: 110
hey Ron, no worries about starting an argument. We are just sharing different perspectives and frankly, I don't mind arguments in any event so long as they are civil and grounded in fact. Beyond which, being challanged (respectfully of course) is how I learn and I think the back and forth is helpful to the larger community.

Yes, I agree, some of the things on my list are of little importance which is why I prefaced the list by stating “some of which matter to coral health and appearance, some are just a personal preference of the hobbiest, and some are of little use or are actually unhelpful and misleading.” My goal was to represent all of the factors that not only I think are important but that I often see being considered. I did not attempt to rank them, other than #1.

My contention is that even though PUR in not something that we can directly measure, even though each coral has a slightly different PUR requirement, even though no manufacturer list the PUR of their lights, even though it can be difficult thing to understand, it still is the thing that matters most since it is one thingabout our lights that most directly affects the health of our coral. Ya, maybe its a bit nuanced but that is why I summed up my point by saying, “The point here is that what matters is what specific frequencies of light are produced.” *

I think you are suggesting that, notwithstanding its importance, since we cant measure it, it's a moot point. I am suggesting that even though we can't directly measure it, lets understand and focus on the things that are the basis of PUR... the light frequency created by the fixture.

So maybe there is another way of getting at my point without using PUR directly. As you noted, we do know that coral responds best to ligh wavelengths of about 400nm – 500nm and 630nm -700nm. Different literature sources provide different ranges so I give these numbers as reasonable approximations. These cover the blue, indigo, violet colors on one end of the spectrum and red on the other. For those of you that really want to understand why... it has to do with the absorbtion bandwith of chlorophyll which the zooxanthellae use for photosynthis. We also know that the green, yellow, orange light in the middle of this range have little to no value to coral (even though the human eye tends to see green -yellow the best).

The number one most important thing to consider then is how well the light spectrum delivered by the fixture corresponds the the light spectrum required for coral health. I think this is a very important issue for hobbiests to understand since this issue is one of the differentiators between vendors. Cheaper fixtures, the “black box” variety, tend to produce a full spectrum of light much of which is uneccessary for your coral. This is why you see so many people buying these lights and then changing the emitters to replace undesirable ones for better ones. Higher-end lights tend to do a better job of targeting the output spectrum to the specific needs of coral. That said, you still find green emitters in higher end lights which isn't entirely bad since it does contribute to what we humans interpret as brightness, but your coral doesn' care much.

Bottom line, regardless of what fixtures you are comparing, compare the spectrum of light the fixture produces with what sectrum of light your corals find useful and choose the fixture where these two are most aligned.

Ill share my anti PAR bias in my next post,betyi all can't wait...teehehe


rfurst is offline   Reply With Quote