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.
Glad to hear it and I always try to keep it civil.
Beyond which, being challanged (respectfully of course) is how I learn and I think the back and forth is helpful to the larger community.
I couldn't agree more!
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.
OK, that makes sense.
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.” *
Except that whether they are cheap or high end, most led fixtures don't offer a spectrum breakdown of their fixtures. And even if some emit wavelengths that really aren't helpful, are they harmful? My best guess is not very if at all, so it's really not a big issue.
I think you are suggesting that, notwithstanding its importance, since we cant measure it, it's a moot point.
Not at all! I think PUR is quite important to understand. But I am saying that I don't think it needs to be considered in buying any of the current led fixtures available in the trade. Most fixtures use quality leds that are powerful enough (like 3 watts or more). And there really isn't enough difference in any of them to make it worth worrying about in your purchase decision. I don't care who makes the 460nm led, Cree, Bridgelux, Epistar... whoever. Or for that matter the bin number of the led. I want an led that is putting out light in and around the wavelength of 460nm. Whether it has a spread from 455nm to 465nm ot a spread from 440nm to 480nm isn't really going to make any difference to my corals. And how many 460nm leds are over my tank? Are there any variations in them? I assume they are all a bit different and I think that is a good thing.
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.
The only thing you really have to judge the light emitted by a fixture is by the stated wavelengths of the leds. And there just isn't that much difference between the MarsAqua ($90) and the EcoTech Radion ($750). I think if you are really concerned about the total output of your fixture, the important difference is that the inexpensive fixtures have 2 channels, blue vs white (with a couple reds and greens) and higher end fixtures (now even the ReefBreeders Photon V-2) that have multiple channels so you can control each color individually. And it's cool if you really think it makes a difference. But I've had EcoTech Radions and inexpensive Chinese boxes and I don't see enough difference to pay the $650 price difference.
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).
No, I don't know that these wavelengths are of "little or no value" to the corals. I'll agree they have little or nothing to do with photosynthesis. But they may, and probably are important to the corals production of color pigments which protect the coral and make them colorful to our eyes. It isn't all about zooxanthellae and photosynthesis.
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't care much.
Just a comment. First you say that cheaper black boxes produce full spectrum... much of which is unnecessary and a couple of sentences later you say higher end fixtures do a better job of targeting output... you still find green emitter in higher end lights. I disagree about the inexpensive fixtures being wrong by doing 'full spectrum' and agree that both the inexpensive and the expensive fixture manufacturers all do it. They just really aren't that different.
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.
I have used both $750 EcoTech Radions and $150 EverGrow (OceanRevive and ReefBreeders) fixtures. Other than one having individual channels for each color led and the other having 2 channels of control, blue and white, there just isn't that much difference. You can make the Radion look different to our eyes by dropping out some of the unnecessary wavelengths for photosynthesis, but that may be dropping wavelengths useful to coral pigment production. But as far as coral health and coral growth, I just don't see anywhere near enough difference to justify the huge cost difference.
