I have a reef light but groups in in saying that they only need blue to grow and white will not help. I was told that blue light is just for show when it comes to coral.
Yeah, a lot of people are unfortunately misled on what is important for corals with lighting and with the white vs blue light thing (to be fair, learning about lighting can be tough because a lot of info out there on lighting is, purposefully or otherwise, misleading/obscured by a bunch of technical terminology that is difficult to learn without help).
All of that to say, for the simplest course of action, I'd suggest picking which color you like the look of (white or blue) and running that color during the times you'll typically see the tank.The study below tested Acropora variabilis and Porites lutea harvested from 2-6 m deep at maintained 6 m deep; they compared dark (no light), full-spectrum (the control), and blue light settings at 200 μmol and 400 μmol (they tested full-spectrum at 800 μmol as well, but 400 μmol was the highest they could get the blue); they used a metal halide light with polycarbonate filters to control what spectrum the corals were being exposed to - the corals grew (calcified) fastest under the blue light, but there was more photosynthesis under the full-spectrum (white) light:
"The light to dark calcification ratios of A. variabilis under 400 μmol photons m−2 s−1 of control and blue light were 8.4 and 10.5, respectively; while lower ratios were observed in P. lutea (3.4 and 4.5). In both cases, calcification under blue light exceeds even these of the control"
Frontiers | Light Enhanced Calcification in Hermatypic Corals: New Insights from Light Spectral Responses
Light enhanced calcification (LEC) is a well-documented phenomenon in reef-building corals. The main mechanism proposed for LEC is that photosynthetic CO2 up...www.frontiersin.org
So, under controlled PAR with metal halides, these shallow water corals grew faster under blue light than white, but but photosynthesis decreased drastically under blue light when compared to white.
To contrast with that, though, another study (using three different species of Acropora - A. tenuis, A. muricata, and A. intermedia at 100 μmol and 200 μmol [low numbers, I know] with LED's) compared different spectrums (the first link below) and found that the inclusion of some red light drastically increased the growth rate (the second link below; the green/yellow spectrum made a little bit of difference, but they didn't add much of it in with any of the three spectrums used; it may have made a bigger difference at higher intensities):
The actual study:
Another contrasting study - Stylophora pistillata from shallow (3 m) and deep (40 m) waters; the shallow specimens showed the highest photosynthesis rates under full-spectrum lighting, but the deepwater specimens showed the highest photosynthesis rates under blue lighting (sadly, they didn't measure growth rates, and the study only took place between March and April, so it was rather short, and results may have changed if the study had been longer).
The spectral quality of light is a key driver of photosynthesis and photoadaptation in Stylophora pistillata colonies from different depths in the Red Sea
SUMMARYDepth zonation on coral reefs is largely driven by the amount of downwelling, photosynthetically active radiation (PAR) that is absorbed by the symbiotic algae (zooxanthellae) of corals. The minimum light requirements of zooxanthellae are related to both the total intensity of downwelling...journals.biologists.com
So, does blue light grow Acropora or other SPS faster than full-spectrum (white) light? It depends on the coral (both species and individual specimen), the location and depth/temperature the coral is from, what light the corals are photo-acclimated to (a shallow water coral growing under blue light in a hobbyist tank for 5 years is likely going to be acclimated to blue light despite its origins), year-round weather conditions (storms and such play a big role in determining what light is reaching the water), the clade of zooxanthellae they're using, etc.
Does the kind of light used (metal halide vs t5 vs LED, etc.) make a difference, or is it all in the spectrum, intensity, and photoperiod? I don't think we'll be able to answer this unless someone is able to make LED's with the exact same spectrum as those other types of lighting, but I'd guess any differences would be minimal.
So, lots of different things go into the growth, and again, fast growth doesn't necessarily equate to excellent health/coloration (it might, but it also might not). Does each coral species have it's own optimal spectrum for growth/health/color? Probably, but I doubt it would perfectly match a different species own optimal spectrum, so I don't know that it would much matter in our tanks - instead, we'd need to find the optimal spectrum for a broad range of corals, which may not be optimal for any particular coral we keep:
"Zooxanthellate corals display contrasting photoacclimation responses, coral cover, colony morphologies and genetic richness along depth gradients33,49,50,51,52,53,54, which collectively suggest that coral species occupy different light niches."
Photosynthetic usable energy explains vertical patterns of biodiversity in zooxanthellate corals - Scientific Reports
The biodiversity in coral reef ecosystems is distributed heterogeneously across spatial and temporal scales, being commonly influenced by biogeographic factors, habitat area and disturbance frequency. A potential association between gradients of usable energy and biodiversity patterns has...www.nature.com
Personally, I'd expect to see similar (not the same, but similar) growth rates from a lot of corals under both blue and full-spectrum lights; some will likely do better under one than the other, but determining which is a lot of effort.
For that reason, like I've said before, at this point in time (barring a major, undeniable scientific breakthrough with our knowledge of corals and light), I would personally only suggest running the windex blue tanks if you really want to see the coral fluorescence pop (as mentioned by others, though, the colors may be best in the long run if you run different spectrums than just blue throughout the day). Like many others have mentioned in various forms by this point, I'd personally run a full-spectrum (white) light that leans somewhat more toward the blue side of things. Is that the "best" spectrum? Maybe, maybe not, but it seems like a good, safe place to start from.
Thanks for everything.
