- As we know
most corals contain tiny single celled organisms
called Symbiodinium.
These are actually dinoflagellates.
Yep, those snotty bubbly scourges of so many reef tanks.
But they're not that kind of dinoflagellate.
They're a helpful kind that uses chlorophyll
just like a plant to produce food for itself,
and it gives some of that food back to the coral
that it lives inside.
Hi, guys and girls, I'm ReefMan.
And this time around we're talking about light spectrums
and exactly how it impacts your coral.
With today's modern LED fixtures,
you can often tune your lights to whatever color you like.
If you want them red,
set it that way,
green,
blue.
You can really do whatever you like with your lights.
But what is best for your coral?
Light at the wrong color or intensity
will severely impact the health of your coral.
And after all the coral's really the reason why
we spend all that money on those fancy lights.
Being able to set our LED fixtures
to some specific color like I was doing,
is really just icing on the cake.
Think of it as a party trick.
What's best for your eyes is not going to be
what's best for the corals in a lot of cases.
Let's get back to those dinoflagellates.
I mentioned that they're using chlorophyll
to produce food just like a plant does.
There's a bunch of different kinds of chlorophyll,
but the two most common in our coral's Symbiodinium
are Chlorophyll-A and Chlorophyll-C2.
Knowing that,
we can do a quick bit of research
and find that Chlorophyll-A has an absorption peak
around 465 nanometers,
and another one at 665 nanometers,
while Chlorophyll-C2 has just one absorption peak
around 449 nanometers.
You may recall that white light, white sunlight,
is really just made out of a mix of colors
all coming from the sun.
If we put the light through a prism,
we can actually see that rainbow of color,
the light spectrum.
If we think of light as a wave of energy
coming from the sun,
each color has a slightly different wavelength.
That's just the distance between the peaks of the waves.
We measure those wavelengths in nanometers
and that's just one billionth of a meter.
Chlorophyll-A responds to two different wavelengths,
about 465 nanometers,
which is a very deep blue violet color,
and 665 nanometers,
which is kind of an orangy red.
Chlorophyll-C2 responds to only one light color
around 449 nanometers,
which is just a violet blue color.
If we look at the data sheets for popular LED lights,
you can see that the LEDs that they're using
often match those colors.
Remember, of course, at 450 nanometer royal blue LED
mainly puts out that wavelength,
but it also provides some below and some above it
probably covering Chlorophyll-A's 465 nanometer peak
as well.
Similarly, a red LED will likely excite
Chlorophyll-A's 665 nanometer peak.
So it does make sense to look at the light spectrum
that's produced by a light that you're interested in,
just to ensure that it covers those peaks.
And of course you shouldn't program it in a way
where you just turn off all the red LEDs
and you don't give the coral that color.
Don't take my word for it though.
There's a paper that looked at exactly this
published back in 2007 titled
"Evaluation of artificial light regimes
and substrate types for a query of propagation
of the staghorn coral Acropora solitaryensis."
There's a link down below in the description
if you want all the nitty-gritty details.
But they tested the growth
and survival of Acropora solitaryensis
using four different metal halide bulbs,
a 5500 K,
a 10 K, a 14 K
and a 20 K.
They also tested two different substrates
onto which their frags were glued using superglue,
they tested concrete and marble.
The team measured the weight of the corals
adjusting with marble or cement tiles
that didn't contain corals,
just to ensure that their results wouldn't be affected
by something leaching out of the substrate.
They measured this weight every five days for 85 days
and remove frags that died at each weighing.
Interestingly,
the paper contains the spectrum of each bulb
that they were using.
Remember they're metal halide bulbs.
And you can see the highlighted bands
were Chlorophyll-A responds over that spectrum.
See how the 5500 K bulb
doesn't really have peaks anywhere at all except red,
and how the 20 K has large peaks down in violet blue
and the small bump also in red.
That's what you want your lights spectrum to be.
You want to have peaks in the ranges
that your coral can actually use,
like that 20 K bulb has.
The team found that the substrate
the coral was attached to
didn't really matter at all,
but the color of the light had a significant impact
on the health and the growth of the corals.
5500 K
and 10000 K metal halide light
was the worst with only 52% of coral surviving at all.
20000 K light with the peaks in the proper places
was the best with 83% of fragments surviving
to the end of the study.
Light also strongly impacted the corals growth.
Acropora frags under 14 K and 20 K bulbs grew much more
than the tanks under 5500 K or 10 K tanks.
Now, this study was done back in 2007
when there was still very much a question
as to if LEDs could grow coral at all.
Of course we know today
that LEDs will work just fine.
And I bet most of you have LEDs over your reef tanks
at home right now.
It's important to consider
just how we tune those lights though,
how we program them.
Make sure you don't completely turn off the red LEDs
and also make sure that the blue,
and the violet, and the royal blue LEDs are also on.
This might end up looking a little bit more blue
than you would usually program to your eyes.
But the coral will thank you
with a better survival rate
and overall better growth.
LEDs tend to produce a very small range of color
centered on a specific wavelength,
and they're sold as royal blue, red,
et cetera, things like that,
just on that one single, central, wavelength.
Take a look at how you've programmed your lights
with this in mind.
You wanna have peaks in intensity around violet and blue,
and also some on the other end around red.
Make some adjustments if you need to.
I think your corals will reward you
over the next few months.
I hope you enjoyed the video.
Please subscribe if you haven't already,
and I will see you next time.
Bye.