Lighting spectra, Photosynthesis, and You Hello all. Some of you may recognize me from Nano-reef and my posts about LEDs, DIY recommendations, etc. Figured I'd post this up over here, as well. Putting it in general hardware and lighting because it applies to more than just LEDs. With full-spectrum LED arrays becoming all the rage nowadays for better coloration, more and more people are considering them, but I see people saying all the time "dude, but corals only use blue light for all their energy and red only helps algae grow, ur an idiot if you add red light" (direct quote from one user). This is just not so. Here is a paper called "Photosynthetic Pigments of Symbiotic Dinoflagellates (Zooxanthellae) from Corals and Clams" by S.W. Jeffrey and F.T. Haxo, 1968. You can find the PDF file here: http://www.biolbull.org/content/135/1/149.full.pdf In it, there is a pretty staggering amount of in-depth information to read through. Iâ€™m going to sum it up and kinda generalize the best I can, so here goes! Corals contain a colorful symbiotic dinoflagellate called zooxanthellae that performs photosynthesis, providing the coral with energy (but does not fill the corals needs 100%, only energy, all corals need to be fed, but thatâ€™s another post for another day). These contain pigments of certain colors that absorb light. The biggest players involved are chlorophyll a and chlorophyll c, peridinin, and neo-peridinin (notice no chlorophyll b, which is not present in zooxanthellae like it is in terrestrial and freshwater plants). These are the bulk of pigments contained in most zooxanthellae (listed in order of highest population), their spectral maximas (the peak absorption wavelengths), and the color they reflect back. The wavelengths are essentially the average of what is presented in the article, with the range usually ~4nm or so. They were taken from many specimens, including Tridacna gigas, Tridacna crocea, Hippopus hippopus, Pocillopora sp., Amphidinium sp., and Peridinium cinctum. [now, you might be wondering 'if these pigments are so colorful, why is it that when corals are starved of light and build up zooxanthellae numbers, why do they turn brown instead of, say, green or red? Well, zooxanthellae typically contain two or more of these pigments - what do you get when you mix blue-green and brick red? brown. ] Chlorophyll a outnumbers chlorophyll c ten to one in zooxanthellae in corals, but in tridacnid clams, chlorophyll c is present at two-thirds chlorophyll a, making it much more prevalent. Peridinin and neo-peridinin constitute 77-84% of total carotenoids present and are considered true accessory pigments to chlorophyll, as they are always present alongside chlorophyll. As you can see by the wavelengths provided above, violet and blue light makes up 100% of the carotenoid absorption maximas, but in chlorophyll, violet is the most important spectra, and red spectra is nearly as important as blue spectra. The bulk of photosynthesis comes from chlorophyll, so Iâ€™d think twice about not including red spectra in your lighting. This can be somewhat proven using good old metal halides â€“ people always say â€œuse 10K for growth, 20K for colorâ€, which makes sense, as a 10K bulb will have more red spectra than a 20K, which will emit nearly all of its energy in the 420-460nm range. When it comes to LEDs, we can pick specific wavelengths we want to add. It started off with cool white (7-10,000K) and royal blue (445-455nm) (and some Chinese fixtures use cool blue instead of royal), and now we recommend to use neutral white (4-5000K) and royal blue, with full-spectrum fixtures bringing in deep red (660nm), cool blue (465-475nm), cyan (495-520nm), and true violet (400-430nm, so no UV). After picking through this article, I'm convinced that royal blue is not nearly as critical to the growth of corals as we imagine, and put into our fixtures. Violet, deep red, and cool blue are the most important, in that order. That being said, most royal blue LEDs will touch on the higher violet peak of chlorophyll a, but not as strongly as a true violet LED will. This is one reason I prefer using Luxeon Rebels for my royal blues, as their peak is at 445nm, so closer to hitting chlorophyll a's peak than Cree XT-E that peak at 455nm. The violet LEDs I would use are split half and half - Steve's LEDs sells SemiLED chips that are 410-420nm, with the peak at 417nm - right on target! In addition, LEDgroupBuy has a new custom bin of violet (not sure what Milad is going to call it yet) that will be available for sale within one week, it registers its peak at 430nm, which hits the OTHER big peaks in violet! I still recommend having neutral white and royal blue in a 1:2 ratio, but I think adding more cool blue and more violet is very beneficial. A word of caution on both - too much cool blue can give a Windex-like look to your water, and too much violet can very easily bleach your corals, so keep them on their own dimmable drivers! Since true violet LEDs hit such peaks within photosynthetic spectra, the PAR value they put out is great, but since they are so close to being ultra-violet, our eyes simply cannot see most of the light they emit, so they appear dim, which makes it easy to add more and crank them up because it's like you can't tell they're even on. I have firsthand experience with this, for the first several months of my tank I could not keep SPS corals, they would all bleach out within a week or two of putting them in the tank from what I now know was too much light, but as soon as I started turning my violet LEDs down, I was able to keep them. Then again, I was using 16x true violet at 700ma over a 55g. A bit overkill in comparison to the eight I would recommend to use now. Hope that helps to shed a little light on the subject (pun intended ). If you have any questions or need any clarification, or advice on what LEDs you should use, let me know, and if you have anything you'd like to add, go for it.