Lighting spectra, Photosynthesis, and You (new plots!)

[BradVincent]

Good article.

 

Have you read:

http://www.advancedaquarist.com/2008/12/aafeature1

 

This seems to contradict “use 10K for growth, 20K for color”, or what I more commonly hear, which is that the 6500k Iwasaki is the best bulb for growth. The 20k bulbs being better for growth is more in line with my experience, and it seems interesting that the growth measured was inverse to the amount of red light.

 

After picking through this article, I'm convinced that royal blue is, in fact, not critical to the growth of corals.

Some people have gotten very good growth with just cool white and royal blue LEDs.

 

I have never argued that red light does not stimulate Chlorophyll a or that it has no effect, just that it is unnatural and possibly harmful. Corals do just fine in nature without it, and I don't think the purple tanks (Mix violet, blues, and reds, what else do you get) that I see look like the ocean.

 

Humans live under a certain spectrum of light. Too much (within reason), too little or the wrong spectrum of visible light has no effect as long as we have a small amount to see by, and can make (or eat) enough vitamin D. Very long (radio) wavelengths are completely harmless and have no effect, but much shorter wavelengths (Gamma rays) will kill us quickly. X-Rays, UV, infrared and microwaves can be harmful but show no immediate effect. If we were abducted by aliens, I'd hope they understood this, and if they didn't, that they would try to reproduce our natural environment, rather than dosing us with Gamma rays hoping it might help us with Vitamin D.

[jedimasterben]

Good article.

 

Have you read:

http://www.advancedaquarist.com/2008/12/aafeature1

 

This seems to contradict “use 10K for growth, 20K for color”, or what I more commonly hear, which is that the 6500k Iwasaki is the best bulb for growth. The 20k bulbs being better for growth is more in line with my experience, and it seems interesting that the growth measured was inverse to the amount of red light.

 

 

Some people have gotten very good growth with just cool white and royal blue LEDs.

 

I have never argued that red light does not stimulate Chlorophyll a or that it has no effect, just that it is unnatural and possibly harmful. Corals do just fine in nature without it, and I don't think the purple tanks (Mix violet, blues, and reds, what else do you get) that I see look like the ocean.

I have not seen that - frankly I don't have much information on halides for the fact that even when I got into the hobby, they were old news. I have talked with many LFS and many hobbyists that have said they get better growth with lower-kelvin bulbs, but that may just be the placebo effect.

 

Any light is harmful to coral. I can bleach a coral by using green light only. Too much light is what is harmful, and can just as easily happen with blue and violet spectrum. We as hobbyists have shown that red spectrum is indeed beneficial, not just in coloration. And think of how many corals live at 10 feet or so (and clams, as well). They are subjected to a nice amount of red and aren't harmed by it. Just because a coral is typically found in deeper water doesn't mean it can't thrive if higher up in a wider-spectrum light.

 

As for CW/RB setups, sure they'll grow coral. Will the grow coral better than if, say, they replace the royal blue with only violet? I doubt it. It looks better that way (though not optimal), but it's still only hitting the downward curve rather than at the peak. And FWIW, none of our lighting types will mimic what is found in the ocean even close to exact.

[HVani]

What about the maxspect razor? I know they are using Warm White.

[jedimasterben]

What about the maxspect razor? I know they are using Warm White.

That's really one of the only ones in that category that I'd recommend using. They use specialty Epistar violet, as well.

[Paleoreef103]

That's really one of the only ones in that category that I'd recommend using. They use specialty Epistar violet, as well.

Agreed. They don't have a much spectrum in the red range so they're not perfect, but they are very good premade fixtures especially for the price. I'd love to get my hands on their dual-core 410-420 nm violets.

[BradVincent]

I have not seen that - frankly I don't have much information on halides for the fact that even when I got into the hobby, they were old news.

 

This from someone who posted research from 1968

 

 

Any light is harmful to coral. I can bleach a coral by using green light only. Too much light is what is harmful, and can just as easily happen with blue and violet spectrum.

 

Yes, but we don't understand yet what "too much" is. Which is why I recommend trying to model natural sunlight.

 

 

We as hobbyists have shown that red spectrum is indeed beneficial, not just in coloration.

 

At best we as hobbyists have produced anecdotal evidence going both ways.

 

 

And think of how many corals live at 10 feet or so (and clams, as well). They are subjected to a nice amount of red and aren't harmed by it.

 

At 10 feet, 640nm is cut in half, and everything longer is cut even more. If you want to simulate 10 feet down, you need a ton more yellow and green than I've seen anyone use.

 

Just because a coral is typically found in deeper water doesn't mean it can't thrive if higher up in a wider-spectrum light.

A coral might do better above the depth it is normally found, but it might also die or bleach out - we don't know. Generally, captive animals do best in conditions closest to their natural environment. I think we have pretty good evidence that corals do adapt themselves to the conditions of the light they grow under.

[jedimasterben]

Agreed. They don't have a much spectrum in the red range so they're not perfect, but they are very good premade fixtures especially for the price. I'd love to get my hands on their dual-core 410-420 nm violets.

The SemiLED that Steve sells should be about the same, as the 'dual-core' chips' peaks aren't exactly at 410nm and 420nm.

 

This from someone who posted research from 1968

A bit of age on me.

 

Yes, but we don't understand yet what "too much" is. Which is why I recommend trying to model natural sunlight.

I see what you are saying, but it is very hard to put a number on what is 'too much' at a specific wavelength, as it would be different for all corals, but as long as the corals are adapted to the light slowly, they should be able to stand (and possibly thrive in) higher output at specific wavelengths.

 

At best we as hobbyists have produced anecdotal evidence going both ways.

Of course. There's always at least two sides to the fence.

 

At 10 feet, 640nm is cut in half, and everything longer is cut even more. If you want to simulate 10 feet down, you need a ton more yellow and green than I've seen anyone use.

Right, but there is still much more than at 20 feet, or 60 feet, and is probably still more red than we put into our fixtures with neutral whites and deep reds.

 

A coral might do better above the depth it is normally found, but it might also die or bleach out - we don't know. Generally, captive animals do best in conditions closest to their natural environment. I think we have pretty good evidence that corals do adapt themselves to the conditions of the light they grow under.

As long as it is done slowly, most corals can tolerate much more light than they were previously under (up to the point of photoinhibition, which I think starts around 700 PAR or so?), which is a wonderful thing in a hobby with so very many different types of lighting.

[Paleoreef103]

As long as it is done slowly, most corals can tolerate much more light than they were previously under (up to the point of photoinhibition, which I think starts around 700 PAR or so?), which is a wonderful thing in a hobby with so very many different types of lighting.

Photoinhibition depends on the taxa. Shallow water acroporas can take 1100 PAR, some LPS will reach that at 300-400 PAR, and clams don't actually have an upper limit. Most corals grow extremely very well at 300-500 PAR.

[BradVincent]

p to the point of photoinhibition, which I think starts around 700 PAR or so?

The point of photoinhibition varies, but I would think it would be below 700 PAR for most corals we keep:

http://www.advancedaquarist.com/2007/3/aafeature1

 

Full sunlight in the tropics is about 2000 PAR, and my spreadsheet puts me about half that for my 10 meter deep build, and almost 80% at 3 meters. Of course that might not be accurate, but I don't see how you could be under 700 PAR at 10 feet of clear water.

[jedimasterben]

Photoinhibition depends on the taxa. Shallow water acroporas can take 1100 PAR, some LPS will reach that at 300-400 PAR, and clams don't actually have an upper limit. Most corals grow extremely very well at 300-500 PAR.

I was speaking of the 'general' amount where corals would start. The acros growing on the reef crests that get exposed at low tide can take a whole lotta PAR.

 

And young clams do - get light too intense and it can kill them.

[kgoldy]

Ben, have you come across any experiments showing the same coral exposed to different wavelengths to find out how this effects growth patterns?

 

Some terrestrial plants respond to blue heavy light by growing taller, because the lack of red tells them they have a canopy to break through. Red causes them to grow wider, since they "think" they've already grown taller than their competitors.

 

(This is on my phone, sorry for not elaborating on the thought and posting links. Just wanted to get the idea out before I forget.)

[jedimasterben]

Ben, have you come across any experiments showing the same coral exposed to different wavelengths to find out how this effects growth patterns?

 

Some terrestrial plants respond to blue heavy light by growing taller, because the lack of red tells them they have a canopy to break through. Red causes them to grow wider, since they "think" they've already grown taller than their competitors.

 

(This is on my phone, sorry for not elaborating on the thought and posting links. Just wanted to get the idea out before I forget.)

I haven't seen any for coral, no, but I'd imagine growth would not be different (other than higher or lower on peak wavelengths). Typically they respond by fluorescing or adapting their colors to help protect from the new type of light, I've never read that their growth would be a different pattern.

[Cintax]

Ben, have you come across any experiments showing the same coral exposed to different wavelengths to find out how this effects growth patterns?

 

Some terrestrial plants respond to blue heavy light by growing taller, because the lack of red tells them they have a canopy to break through. Red causes them to grow wider, since they "think" they've already grown taller than their competitors.

 

(This is on my phone, sorry for not elaborating on the thought and posting links. Just wanted to get the idea out before I forget.)

 

This is the principal behind using metal halide bulbs for vegetation and high pressure sodium bulbs for flowering when growing "tomatoes" indoors.

[kgoldy]

This is the principal behind using metal halide bulbs for vegetation and high pressure sodium bulbs for flowering when growing "tomatoes" indoors.

 

 

Yes. Yes it is.

[boxboy]

So what about those of us who are not very Handy. Is there a LED fixture on the market that seems to have this true full spectrum that corals need?

 

Does this not count for "Full Spectrum" Or better? and not DIY!

 

Epistar LED Chips

2x 4500k Neutral White

4x 455nm Royal Blue

2x 470nm Cool Blue

1x 495nm Turquoise

1x 660nm Deep Red

2x 410nm Pure Violet --> Looking into getting that 3w dual 410nm/420nm voilet! same as the maxspect.

Dimmable – Yes

 

Maybe Jedi can comment on this?

[uglybuckling]

I assume that's the Bright Aquatics bulb you're linking the specs to? It's a great bulb, and it definitely qualifies as full spectrum.

 

I think Jedi was referring to fixtures larger than a PAR38 bulb when he said there wasn't much out there. I know about the Radion, some of the Reefbreeders fixtures, and these: http://www.nano-reef.com/forums/index.php?showtopic=313348

 

That's about it in terms of fixtures (not bulbs) that offer full spectrum with neutral whites and reasonably okay ratios. That I know about. Does the Radion even use neutral whites? I'm not recalling right now.

[boxboy]

I assume that's the Bright Aquatics bulb you're linking the specs to? It's a great bulb, and it definitely qualifies as full spectrum.

 

I think Jedi was referring to fixtures larger than a PAR38 bulb when he said there wasn't much out there. I know about the Radion, some of the Reefbreeders fixtures, and these: http://www.nano-reef.com/forums/index.php?showtopic=313348

 

That's about it in terms of fixtures (not bulbs) that offer full spectrum with neutral whites and reasonably okay ratios. That I know about. Does the Radion even use neutral whites? I'm not recalling right now.

 

Yes, then I must aggree that there is not many full size fixtures that qualify as full spectrum, and even less big box companies using NW leds. some larger compaines are starting to see the light lol but still a while to wait.

Till then DIY all the way. Enless your able to find somone or company that will custom a fixture just for you and not charge your a crazy amount!

 

Whats excatly are people looking for in terms of full spec or half spec pre-built fixtures?

I know with all the crazy gizmoes out there that some DIY are just amazing.

[blasterman]

and even less big box companies using NW leds. some larger compaines are starting to see the light lol but still a while to wait.

 

They don't use neutrals because the Chinese coulnd't make a decent neutral phosphor if their life depended on it. The difference in quality between a 85CRI name brand bridgelux Neutral or Rebel ES -vs- a Aquastyle neutral is huge.

 

More importantly, cool white rigs show off garish actinic colors better than neutral rigs, and will also show higher artifical PAR numbers. Since they are selling to a market demographic that's 90% under the age of 26 and likely will be in the hobby less than 21months they want to maximize profit. I thought about building Bridgelux Array or Fortimo Linear based lights, and my rigs destroy halides having done the side by sides, but gave up when I saw all the BS out there. Cool white LEDs can be 10,000k or 4500k. That's a lot of deviation room for a light maker to throw whatever LED of the week they can get in there.

 

In regards to zooxanthellae and light spectrum, the white papers are abundant but the actual facts are slim. There has been *no* evidence that yellow, orange, red or far red has a metabolic effect on corals. Very little of this light penetrates water, and hence corals have little evolutionary need for it. Same with UV. Short wavelength blue just confuses the coral, or forces it to produce pigments to protect itself from zooxanthellae getting over stimulated and starving the coral. I've seen a few articles showing orange-red or red light tells a hard coral it's growing too shallow and to spread horizontally. This is why 10,000k or 6500k lights are claimed to have faster SPS growth. The coral is simply growing horizontal -vs- vertical.

 

Zooxanthellae is in constant competition with a coral in terms of food / energy, and most of the time the coral is battlign to keep zooxanthellae from gobbling up nutrients too fast. This is why phosphate kills SPS - phosphate causes zooxanthellae to go crazy and devour all the nutrients in the coral and kills it. Adding a specific spectrum almost never results is a healthier coral unless your light is deficient in the first place. What is known to work for proper and healthy clam and especially SPS growth coral growth is proper nutrient ratios, distributed -vs- highly collimated light sources (good luck convincing you guys of that) and a broad spectrum of blue light from ~450-480nm. The rest has no evidence.

[Dasani]

I still recommend having neutral white and royal blue in a 1:2 ratio

I had this combo and my SPS looked alright, but not as good as I wanted them to. They didn't grow well either. I could take a birdnest out of my tank, put it in my 75g with 20k radiums and it would look 10x better in a month or so and would have grown twice as fast. I don't really understand all LED wave length and all that. I tried LEDs and it was a swing and a miss. I'm back to halides now. I probably wont ever change.

[jedimasterben]

In regards to zooxanthellae and light spectrum, the white papers are abundant but the actual facts are slim. There has been *no* evidence that yellow, orange, red or far red has a metabolic effect on corals. Very little of this light penetrates water, and hence corals have little evolutionary need for it. Same with UV.

And shallow water corals couldn't use it at all? White papers are the closest thing we have to evidence of what corals use for photosynthesis. If it says that the majority of zooxanthellae contain chlorophyll a, with absorption peaks at 410, 430, and 660nm, whether the coral has access to them in the wild is irrelevant if they are capable of using them. If they didn't use any light not in the blue spectrum, then LED-lit coral farms would only be using blue LEDs, and one thing we do know is that that does not work.

 

UV is right - very little penetrates the water. At 15", nearly all UVB is gone, and most of UVA, which is still detrimental to coral health, though in small quantities can possibly cause some fluorescence, but it's not worth the downsides. What we call 'true violet' light are the best - closer to the peaks of chlorophyll a, which is the most highly concentrated pigment in most all corals, than royal blue. I have a list of experiments I wish I had room to run to test things like that.

 

Short wavelength blue just confuses the coral, or forces it to produce pigments to protect itself from zooxanthellae getting over stimulated and starving the coral.

As long as it isn't immediately blasted with the light, it will adapt to it - just like when we bring a coral home, it has to adapt to the new lighting, nothing different than what happens now. Too much blue light can kill a coral just as fast as too much red light.

 

I've seen a few articles showing orange-red or red light tells a hard coral it's growing too shallow and to spread horizontally. This is why 10,000k or 6500k lights are claimed to have faster SPS growth. The coral is simply growing horizontal -vs- vertical.

That's very interesting, I'll have to read up on that.

 

Adding a specific spectrum almost never results is a healthier coral unless your light is deficient in the first place. What is known to work for proper and healthy clam and especially SPS growth coral growth is proper nutrient ratios, distributed -vs- highly collimated light sources (good luck convincing you guys of that) and a broad spectrum of blue light from ~450-480nm. The rest has no evidence.

Unless you can point us to some other study that says corals definitely use 100% 450-480nm, then we have what we have to work with, and it gives specific wavelengths that common zooxanthellae absorb, so that's what we should shoot for. Those are my thoughts on the subject.

 

I had this combo and my SPS looked alright, but not as good as I wanted them to. They didn't grow well either. I could take a birdnest out of my tank, put it in my 75g with 20k radiums and it would look 10x better in a month or so and would have grown twice as fast. I don't really understand all LED wave length and all that. I tried LEDs and it was a swing and a miss. I'm back to halides now. I probably wont ever change.

There's too many variables there that you left out to say that it was your lighting.

[Nano sapiens]

Hi Ben,

 

I read your post on this article: http://www.advancedaquarist.com/2012/10/aafeature

 

about the dangers of adding too much violet intensity to a tank. Did you notice the issues right away or did the damage take time to manifest? What type of damage did you observe?

 

I've added a 405nm Stunner Strip to a shallow 13" nano tank where the light fixture sits 5" above the water surface using a 9 hr operating time. I've had the strip running for the last couple days and I haven't noticed any negative reactions from the corals (so far) and this may well be due to the fact that each LED is only 1/4 watt (24 total). I'm sure the LEDs you used were a lot more powerful.

 

Thoughts?

[jedimasterben]

Hi Ben,

 

I read your post on this article: http://www.advancedaquarist.com/2012/10/aafeature

 

about the dangers of adding too much violet intensity to a tank. Did you notice the issues right away or did the damage take time to manifest? What type of damage did you observe?

 

I've added a 405nm Stunner Strip to a shallow 13" nano tank where the light fixture sits 5" above the water surface using a 9 hr operating time. I've had the strip running for the last couple days and I haven't noticed any negative reactions from the corals (so far) and this may well be due to the fact that each LED is only 1/4 watt (24 total). I'm sure the LEDs you used were a lot more powerful.

 

Thoughts?

The damage happened within a week. The LEDs I used then are significantly more powerful than that stunner strip, the whole strip is probably equal to two or three of the '3w' violets, and I was using far more than that with 60 degree optics. You should be fine.

[Nano sapiens]

The damage happened within a week. The LEDs I used then are significantly more powerful than that stunner strip, the whole strip is probably equal to two or three of the '3w' violets, and I was using far more than that with 60 degree optics. You should be fine.

 

Yeah, that's what I thought. Thxs.

[uglybuckling]

Blaster,

 

I was very interested to read your reply to this thread. There are a lot of folks around here, myself included, who see you as a pioneer in reef lighting, and therefore really value your opinions. As I was reading through, there were a few points that were unclear to me. If any of the stuff below comes off as being argumentative, please understand that it is said with respect, and that I'm probably just confused.

 

They don't use neutrals because the Chinese coulnd't make a decent neutral phosphor if their life depended on it. The difference in quality between a 85CRI name brand bridgelux Neutral or Rebel ES -vs- a Aquastyle neutral is huge.

 

More importantly, cool white rigs show off garish actinic colors better than neutral rigs, and will also show higher artifical PAR numbers. Since they are selling to a market demographic that's 90% under the age of 26 and likely will be in the hobby less than 21months they want to maximize profit. I thought about building Bridgelux Array or Fortimo Linear based lights, and my rigs destroy halides having done the side by sides, but gave up when I saw all the BS out there. Cool white LEDs can be 10,000k or 4500k. That's a lot of deviation room for a light maker to throw whatever LED of the week they can get in there.

 

The marketing BS is a lot to take, very heartily agreed.

 

In regards to zooxanthellae and light spectrum, the white papers are abundant but the actual facts are slim. There has been *no* evidence that yellow, orange, red or far red has a metabolic effect on corals. Very little of this light penetrates water, and hence corals have little evolutionary need for it. Same with UV. Short wavelength blue just confuses the coral, or forces it to produce pigments to protect itself from zooxanthellae getting over stimulated and starving the coral. I've seen a few articles showing orange-red or red light tells a hard coral it's growing too shallow and to spread horizontally. This is why 10,000k or 6500k lights are claimed to have faster SPS growth. The coral is simply growing horizontal -vs- vertical.

I agree that most of the literature and arguments surrounding 'better growth with full-spectrum lighting' are very theoretical at this point, and despite looking for good side-by-sides, I have not found any. I've spent some time thinking about how to set up such an experiment, and may dedicate a thread to it sometime soon. With regard to rendering of corals, and to a lesser degree fluorescence of corals, I think that full-spectrum has a pretty good track record. But for growth? Lack of evidence, I agree.

 

There is, however, a lack of evidence for numerous things that simply make theoretical sense. I would point you to my favorite research paper:

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC300808/

 

Additionally, I come from a million years of human evolution, in which eyeglasses were almost completely absent from my environment, and yet thankfully I have managed to come across some eyeglasses recently and they help me immensely in terms of not walking into things. Certainly I have no *evolutionary need* for eyeglasses, but this does not mean I can't put them to good use.

 

With regard to short-wavelength blue specifically, I was under the impression that plenty of short-wavelength blue was present in most corals' native environment. Again as above, this doesn't mean they can use it, and it doesn't automatically mean that it's helpful (certainly there are lots of harmful things in corals' environments these days). But if they encounter it naturally, how do they deal with it there? How would it confuse them to encounter something that is present in their native environments? In terms of forcing the development of pigments for protection, I was under the impression that that mostly applied to the ultraviolet spectrum (where the light itself is harmful) and not to true violet (where the light is not harmful to tissues directly, but (as you stated) its effects might be to overstimulate zooxanthellae (see below!))

 

Zooxanthellae is in constant competition with a coral in terms of food / energy, and most of the time the coral is battling to keep zooxanthellae from gobbling up nutrients too fast. This is why phosphate kills SPS - phosphate causes zooxanthellae to go crazy and devour all the nutrients in the coral and kills it.

 

(my understanding was that this was related also to use of phosphate in the coral skeleton--from this article, "To summarize, we suggest that a phosphate-induced increase in zooxanthellar populations may cause an increase in photosynthate and expendable energy reserves, and in turn permit increased calcification/growth. The increased photosynthesis would create a higher demand for carbonic anhydrase, thus increasing the pH in the intracoelenteric pace. This would also create a deficit of carbonate available for calcification which in turn would allow the phosphate ions to be used as a supplement to the carbonate ions while simultaneously helping to maintain an optimum pH. A lighter skeleton containing higher levels of calcium phosphate may then be formed, resulting in an increase in coral skeletal porosity."

 

The calcium phosphate skeleton, briefly, is not a good thing. Sort of like osteoporosis for corals.

 

So anyway, is the goal, then, to avoid stimulation of zooxanthellae? I mean, I know that insufficient light makes zooxanthellae proliferate and express green and red accessory pigments (in an attempt to get more light), which, when mixed, make for "browning out." Adequate light makes both zooxanthellae and coral flourish. Too much light, you tell me, makes zooxanthellae proliferate at the expense of the coral. Way too much light, I know, makes the coral bleach as it expels zooxanthellae.

 

So should we strive to keep a minimum amount of zooxanthellae present in the coral's tissues, just barely producing enough sugars to keep the coral alive without having enough leftover energy for the algae itself to proliferate?

 

If the goal really is to essentially keep the zooxanthellae just barely surviving (without proliferating, but without becoming stressed and making a bunch of red and green pigments either), this would make a pretty good cornerstone for an argument against trying to directly stimulate the photosynthetic spectrum utilized by zooxanthellae.

 

If I have not misunderstood the arguments here, then this makes a reasonably compelling theoretical case against addition of spectra that will directly stimulate zooxanthellae.

 

I'm not a die-hard SPS guy myself, so many of the above arguments concern me less than they might concern somebody who really is all about the SPS.

 

distributed -vs- highly collimated light sources (good luck convincing you guys of that)

 

This really interests me, and is not something I've heard much about before. Given my career, in which I use a lot of microscopes, I think of collimated light as being light that has passed through a condenser or lens, and thereby caused to have mostly-parallel rays in a tightly-focused area. With 120 degree optics and fairly reflective glass on the sides of the tank, I think of the majority of (non-lensed) LED light sources as quite unfocused, and by the time the light rays bounce off the walls a few times, would qualify in my mind anyway as "distributed." Certainly without optics, I feel that LEDs come close to other point light sources with wide cones such as metal halides, in terms of how distributed the light is. However, this may still qualify as "collimated" by comparison to a more distributed light source like a fluorescent tube.

 

Regarding the term "distributed light sources," as related to LEDs, were you going for (1) use of a diffuser, or (2) even spacing of the LEDs over the top of the tank? Or both?

 

I'm curious about any theoretical or practical evidence in favor of distributed LEDs. I've wondered about it a few times (like, "what's the downside to all of the clustering we do to avoid disco effect?") and to be honest after looking at tanks lit by power compacts and T5s, I've thought, "I wonder why LEDs can't behave more like these lights." So yeah, let me know! Who knows, you might convince at least one of us.

[blasterman]

If I have not misunderstood the arguments here, then this makes a reasonably compelling theoretical case against addition of spectra that will directly stimulate zooxanthellae.

 

Mmm, the arguement is what light sources should be use that grow coral decently while primarily producing goofy, artifical colors in coral that reefers prefer. Far blue dominant light sources, such as those we are using that center around 450nm aren't going to be negated by fragments of additional colors. Frankly I don't know why we bother using terms like 'full spectrum' for anything other than aethestic reasons because all of the light sources discussed here and elsewhere are 445-455nm dominated with just a smidge of everything else. I have a spectrometer, I've measured countless tanks with it, and nothing discussed on this forum is anywhere near 'full spectrum' in the literal or scientific sense.

 

If we were indeed concerned about full spectrum we'd be using 6000k high CRI T5's (or 5000k rebels)exclusively on our tanks. Nobody would do this because of the nasty color. Corals would otherwise grow great, which is why coral farms often use halides in this color temp rather than six color LED rigs (or 20k halides). While testing SPS reactions to intense LED light I found that 470nm tigtly focused LED light produced the harshest bleaching reaction in SPS, 450nm the second, and cool-white barely at all. All three light sources had nearly identical radiometric intensities of blue light (just different wavelength), but there was an astounding difference in bleaching sensitivity. Corals might not be able to utilize all the wavelengths in white light -vs- blue light, but they sure grow more stable under white light.

 

I'm not a die-hard SPS guy myself, so many of the above arguments concern me less than they might concern somebody who really is all about the SPS.

 

SPS have the fussiest light requirements, that's why I use them as a reference. You can grow LPS and softies fat and happy with the Walmart CFLs.

 

I think of the majority of (non-lensed) LED light sources as quite unfocused, and by the time the light rays bounce off the walls a few times, would qualify in my mind anyway as "distributed."

 

Most of the light distribution in reef tanks occurs due to water ripple at the surface. This is also the only mechanism that allows point sources like halides to be even useable because otherwise they'd produce seriously disjointed and uneven growth in hard corals. So, in a sense the ripple and shimmer that halide owners prefer actually is healthy for the corals because it helps increase the dimensional area that light is coming from. This is very critical for hard corals. Much less so for LPS or softies because their greater tissue area allows zooxanthellae to rapidly migrate to more optimum light angles. Alos, another reason that soties and LPS were initially claimed to be more tolerant of LED light.

 

Otherwise, growing hard corals under narrow angle light cones produces a lot of problems and uneven growth because there's no adaption mechanism for such a light. Lots of water ripple saves the day. Ever sit in the sun in a lawn chair for a couple hours at noon and get a sunburn? You'll get burned on a specific foot, shin, bald spot.....but it's never even. Corals have the same problem with LED lenses.

 

Most severe example of this are Kessil based tanks. Go through some of those threads and you'll see countless examples of SPS growing in narrow stalks and at 45 degree angles to the light source.

 

Best growing SPS tanks I've seen the past half dozen years or so are an even mix of T5 -vs- halide with just a smidge of LED based tanks. I really hate T5 because the lighting is so flat, but reluctantly admit that the broad and even lighting produced by fluorescent tubes produces the fattest and most even growth of hard corals per watt. In terms of LED I'm seeing more and better tanks lit with those cheap, 120watt chinese LED fixtures with bare LEDs than Cree based American fixtures that use optics. If optically pumped up PAR numbers were the only thing that mattered we'd be using lasers to light our tanks. The good thing about multi-spectrum LED approach is more and more tanks using diffusion to blend all the Disney colors together.

 

Side topic, but the past year I've ben focusing more and more on terrestrial agriculture, and had my eyes opened when I finally managed to build LED lights of sufficient power ratios to surpass T5 HO and halides. In short, what we found was blue and red based lights *sucked* compared 4000-3500k kelvin white, and distributed light bars produced way better growth than dense panels.