Could high energy visible (HEV) light be damaging to corals?

By Jake Adams on Jan 12, 2011

High Energy Visible (HEV) light refers to the part of the spectrum from 380-530nm, which includes our beloved blue and royal blue LEDs as well as the violet, indigo, cyan and near-UV LEDs which are not yet widely used. With many reefers currently running heavily blue lighted aquariums and the adoption of LEDs and their superpowers in the blue end of the spectrum, we’ve been quietly concerned about the potential for us to overdose our corals with HEV light.

HEV light has already been implicated as one of the causes of macular degeneration (vision loss) in people. In addition to urging you to use caution when you are near high power blue or purple LEDs, we should also consider how HEV light can affect our reef tanks. We already know that many of our photosynthetic reef animals are sensitive to too much red light, too much light and lights that are on for too long. We also know that photosynthetic pigments get tweaked for higher performance towards the blue end of the spectrum due to the attenuation of sunlight as it penetrates seawater. Therefore it is not a big leap to consider that huge quantities of blue light from multiple emission peaks could be enough to cause some injury to our photosynthetic reef animals.

In working with a variety of blue LED lights over corals, we can at least say that corals react to blue light from LEDs in unexpected ways for the given measured PAR value, and the perceived brightness of the light by our eyes. Hit us up in the comments if you’ve experienced unexpected results using blue LED lights over your corals; we’re particularly interested in hearing from the CoralSky SL2 and blue Ecoxotic LED cannon users since these are some of the highest density blue LED lights currently in the reefing hobby.

http://pulse.yahoo.com/_EHBVE2XVUWI4V6QZIPBBTCJBAU Michaelangelo

I use 3wCree’s and have been for 6 months now. It is 24 total 12 royal blue, 12 white. The only difference I really see compared to my halide tank is the corals are much more vibrant. The blue mille I have growing , well grows slower but it is turquoise. I mean the coral is stunning. But on the other hand my poccilopora instead of a dark body has a whitish body and the polyps are greener than anything ive seen. Those two are the only ones ive seen a change in , the zoanthids etc.. look the same
http://twitter.com/chrisozolins Chris Ozolins

When I read this, I thought “wow, could it be? We’ve been doing it wrong this whole time?”. Then I read further, and discovered this is all speculation without much merit. Relating vision to photosynthesis is a bit of a stretch. Just about as useful as relating a plant growing in your yard to a human being staring at the sun.

Also:
“We also know that photosynthetic pigments get tweaked for higher performance towards the blue end of the spectrum due to the attenuation of sunlight as it penetrates seawater. Therefore it is not a big leap to consider that huge quantities of blue light from multiple emission peaks could be enough to cause some injury to our photosynthetic reef animals.”

Ya, the whole idea is that deeper-water species photosynthetic radiation utilization is geared more towards the shorter wavelength end of the spectrum. How does this directly relate to them being more or less susceptible to light intensity in that wavelength range? They get a tonne of violets and blues naturally…

Don’t get me wrong, I’d love to see some cold hard data, some kind of ideal spectrum and intensity range, but you got me excited over nothing. Too much of anything is often a bad thing, but that’s not news.
Anonymous

Chris I wish we had the data. Fortunately/unfortunately reefers are at the forefront of users of massive amounts of HEV light and this post was drafted specifically to ask the question.

My point about blue-light-tuned photosynthesis is that if we blast it with massive amounts of blue light, it is kind of like putting a amplified microphone to a loudspeaker.
Anonymous

I’ve definitely seen corals bleach from white LEDs in my system, but never from the blue ones.
http://twitter.com/chrisozolins Chris Ozolins

I’m all for asking the question, I’m just wondering where it came from (why now)?

I know we’ve mapped out the point where photosynthetic rate reaches peak efficiency based on insolation with many plants, after which it decreases (potentially all the way to ceasing) while photorespiration increases to soften the blow of photoinhibition. The weird thing is, there are a few studies out there showing how dim light is more damaging as a photoinhibitor than higher-intensity lighting. Lots of species dependent and/or conflicting results. It’s a lot of blah blah blah with photosystem 2 and oxidation… but the core of it all supports the idea that variation in light intensity will effect a plants photosynthetic equilibrium, to the point of degradation even.

You have a valid question, for sure, and photosystems (especially those underwater) are a super interesting subject, I was just wondering what triggered you to ask the question? I think its common sense that a reefer wouldn’t WANT to throw too much light at their photosynthetic corals, but without a paint by colours chart detailing ideal radiation intensities for zooxanthellae by wavelngth, what led you to believe we were harming our corals? I’d love to know the average intensity of visible HEV light in some the more prominent coral export regions and compare them to ours…
Anonymous

After reading the link, I’m more worried about my own eyes! I’m around aquarium lighting 5-10 hours a day!

I think just like any light source, too much intensity can be harmful to corals. I’ve been very successful in keeping Australian A. lordhowensis frags in my growout system under strictly ATI blue plus t5 bulbs. The lights are on 8 hours a day and the color and growth is noticeably better than another tank on the same system with a mix of Aquablue special/ATI Pro Purple/ATI Blue Plus.

The Aquaillumination Blue Sol fixture that I have experience with has also proven itself to support great growth and color. I often stick corals in this tank that have “potential” just to see what they do.

Incidentally, clams and SPS do not do as well in the acan growout tank with only Blue Plus. But they do great under the mix of Aquablue special/ATI Pro Purple/ATI Blue Plus (same water and very similar flow rates). The PAR is a bit higher in the whiter tank, but not a huge difference.
http://pulse.yahoo.com/_TY62P4IMCIOGM5T3WOGV625FII The Jesus

I think it is a good question to ask, even if it is 100% pure speculation. I’m one of those that believe you should question everything.
http://pulse.yahoo.com/_SD4KNGZELKZAJZVLJIQ5QRINXI Fournier

I think this is interesting, however I don’t see why this is much different then any other kind of reef lighting. If you look at a 20K radium the vast majority of it’s output is between 450 and 455nm, right about the same place as a royal blue LED. True the LED has a more narrow range of frequencies produced, but the peak is in pretty much the same place.
Anonymous

I’ve been running a DIY LED rig over my 220 gallon system since August and I am very interested in this subject. For some system background, I have five fixtures of 24 LEDs a piece (120 total) over the 6′x2.5′x2′ system. I use 60 XR-E Royal Blues, 50 XR-E Cool Whites, and 10 XR-E Neutral whites. The LEDs are driven with DIY drivers at 700mA with a full range (0-255) of PWM dimming control. All of the fixtures are 14″ above the water surface with 80 degree optics on the outside LEDs and 60 degree optics on the inside LEDs, and no optics on the center fixture. I don’t know what RB’s policy is on linking pictures, but heres a photobucket link to a FTS (false color) of my PAR readings on full blast. It had more PAR then my T5′s up top, less on the sand bed, and overall I wasn’t too impressed with the numbers:

http://i306.photobucket.com/albums/nn248/Taqpol/82310LightsFTS.jpg

Ryan Brucks, whose LED/T5 hybrid was actually featured on this site months ago warned me that if corals were not properly acclimated to the LED light they would bleach so in August I started out the LEDs at half power using PWM (130/255) and slowly ramped it up from there. By slowly, I mean increasing it by 10 PWM “value points” (~4% of the total light output) biweekly for two months. At the 60-70% range the corals were looking good and encrusting, but as I slowly moved towards higher light levels the corals got lighter and lighter. Two months later around Thanksgiving I had finally gotten the tank to ~210/255 when the ____ hit the fan. I had a minor alk spike that led to burnt tips, and then any corals that were looking stressed by the increased light immediately bleached. Some corals were fine, like a green Acropora samoensis, but others like all my Montiporas (caps and digitatas) and maricultured corals completely bleached.

I’ll be looking for more data on the HEV light hypothesis. I also have a hypothesis of my own, but I don’t know how to test it. I think something to do with optics, specifically tight optics close to the tank, might be the problem. My thought is that focusing and bending the light in that way is causing it to be read less accurately by our PAR meters such that our LED rigs are actually producing much more PAR then we think they are. Potentially this could be due to the PAR meters sensor design where the angle of the light causes it to not fall directly on the sensor depending on the angle you hold it, I don’t know. I immediately dropped my light back down to about 60% and got the alk stable and my corals have slowly been recovering.

Also, there are so many factors that affect coral growth and coloration besides light that I can’t honestly say it was JUST my lights that did it. As I mentioned I did have a slight alk spike near the same time and had just started running biopellets so my nutrients (Nitrate) were higher at the beginning vs. November when everything went bad. A lot of factors seemed to converge all at once for me…
Anonymous

If this theory does have merit, one thing that might play into it is the “extreme” point source light emitted by LEDs. LEDs are becoming powerful enough that an emitter the size of a grain of rice puts out the same amount of light as a MH bulb emits from an emitter the size of a gumball. It’s just a guess, but could it be related to the light coming from such a small, concentrated source?

I say this because I noticed bleaching on some LPS I had situated below a 1W 6500K LED with 40 degree optics in a part of a tank that had very little disturbance of the surface of the water. Once I aimed a powerhead to cause some ripples on the surface of the water to break up/diffuse the light the bleaching stopped….

Just a thought….
Anonymous

Jake, I think this is a great topic. You are always questioning everything, and as a result, we continue to improve the technology and the understanding of our hobby.

Your theory fits in well with something I’ve been contemplating for the last couple of months. A common observation regarding LED lit tanks is the incredible amount of shimmer in the tank. Personally, I believe the shimmer exceeds that of a MH lit tank, and the reason is because shimmer is caused when a point source of light interacts with a moving water surface. The refraction that occurs when the light crosses from the air to water medium, combined with the moving water surface, causes constructive and destructive interference in the “waves” of light in the water, setting up localized bright and dark areas. This effect constantly changes with the movement of the water surface, and the result is a shimmering effect.

This effect occurs in the wild, since the sun is a point light source. This effect also occurs under metal halide and similar point light sources, but is absent (or much less apparent) under distributed light sources, such as VHO and T5 (and cloudy days). With LED systems, we can be talking about dozens (or even hundreds) of point source emitters, each of which is creating this shimmer effect.

Here is where my observations and Jake’s theory may begin to merge, but first, I need to digress a bit more and explain something significant about PAR. This method of quantifying light intensity has become the measurement of choice for the reefing community (rightly so), but due to the complexity of the units of measurement involved, we have become used to hearing this measurement described in units of “PAR”, e.g., “Wow, I measured 200 PAR on my sand bed…that is really cool!”, etc. However, the units of measurement are actually µmol photons/m2/second, and I’m not bringing this up to show you how easy it is to find this on Wikipedia. I’m bringing this up to call your attention to the fact that it is an AVERAGE of µmol photons that falls on a square meter over a SECOND. It’s not an instantaneous measurement! It’s an average, and in a shimmering tank, those “glitter lines” move fast.

Now, the Jake’s out there will already know where I’m headed with this, but it took me a while, so I’ll try to wrap this up with a summary: A measurement taken by a PAR meter of 200 “units” in your tank may hide the fact that instantaneous values of photon flux density may be “off the charts”, as multiple localized bright areas (shimmer), can combine for a fraction of a second over one small area of your coral and significantly exceed the light levels where photoinhibiting occurs.

Since shimmer occurs in nature, I believe that photosynthetic organisms must be able to handle a significant range of light density for very short periods of time. However, when we are talking about dozens or even hundreds of point source emitters, the rate and amplitude (extreme high and low values) of light density falling on a particular spot on a particular photosynthetic organism is likely to be more extreme than that found in nature, or under a couple of metal halide lights, even if the AVERAGE photon flux density occurring over a second is exactly the same.

The bottom line for my hypothesis: 200 PAR may not mean the same thing under every light source. I believe that the extra shimmer produced by LEDs is causing INSTANTAEOUS values of light density, frequently enough, that photoinhibition (bleaching) is occurring, even under PAR values that do not seem excessive for a particular species.

I don’t believe this is a warning sign that LED may be a poor choice for lighting our reefs. In fact, I think this phenomenon may actually be another tick in the plus column for LED lighting. You may only need 150 PAR instead of 200…
Anonymous

Jake, I think this is a great topic for discussion. You are always questioning everything, and as a result, we continue to improve the technology and understanding of our hobby.

Your theory fits in well with something I’ve been contemplating for the last couple of months. A common observation regarding LED lit tanks is the incredible amount of shimmer in the tank. Personally, I believe the shimmer exceeds that of a MH lit tank, and the reason is because shimmer is caused when a point source of light interacts with a moving water surface. The refraction that occurs when the light crosses from the air to water medium, combined with the moving water surface, causes constructive and destructive interference in the “waves” of light in the water, setting up localized bright and dark areas. This effect constantly changes with the movement of the water surface, and the result is a shimmering effect.

This effect occurs in the wild, since the sun is a point light source. This effect also occurs under metal halide and similar point light sources, but is absent (or much less apparent) under distributed light sources, such as VHO and T5 (and cloudy days). With LED systems, we can be talking about dozens (or even hundreds) of point source emitters, each of which is creating this shimmer effect.

Here is where my observations and Jake’s theory may begin to merge, but first, I need to digress a bit more and explain something significant about PAR. This method of quantifying light intensity has become the measurement of choice for the reefing community (rightly so), but due to the complexity of the units of measurement involved, we have become used to hearing this measurement described in units of “PAR”, e.g., “Wow, I measured 200 PAR on my sand bed…that is really cool!”, etc. However, the units of measurement are actually µmol photons/m2/second, and I’m not bringing this up to show you how easy it is to find this on Wikipedia. I’m bringing this up to call your attention to the fact that it is an AVERAGE of µmol photons that falls on a square meter over a SECOND. It’s not an instantaneous measurement! It’s an average, and in a shimmering tank, those “glitter lines” move fast.

Now, the Jake’s out there will already know where I’m headed with this, but it took me a while, so I’ll try to wrap this up with a summary: A measurement taken by a PAR meter of 200 “units” in your tank may hide the fact that instantaneous values of photon flux density may be “off the charts”, as multiple localized bright areas (shimmer), can combine for a fraction of a second over one small area of your coral and significantly exceed the light levels where photoinhibiting occurs.

Since shimmer occurs in nature, I believe that photosynthetic organisms must be able to handle a significant range of light density for very short periods of time. However, when we are talking about dozens or even hundreds of point source emitters, the rate and amplitude (extreme high and low values) of light density falling on a particular spot on a particular photosynthetic organism is likely to be more extreme than that found in nature, or under a couple of metal halide lights, even if the AVERAGE photon flux density occurring over a second is exactly the same.

The bottom line for my hypothesis: 200 PAR may not mean the same thing under every light source. I believe that the extra shimmer produced by LEDs is causing INSTANTAEOUS values of light density, frequently enough, that photoinhibition (bleaching) is occurring, even under PAR values that do not seem excessive for a particular species.

I don’t believe this is a warning sign that LED may be a poor choice for lighting our reefs. In fact, I think this phenomenon may actually be another “tick in the plus column” for LED lighting. You may only need 150 PAR instead of 200…
Anonymous

Sorry about the double post. This whole disqus, FB connect thing got me all confused…
http://www.facebook.com/profile.php?id=100000691010948 Rainbow Reef Corals

Hmmm, this is interest. We aren’t totally set on these leds, quite yet.

WERE GIVING AWAY FREE CORALS – sign up!
http://www.rainbowreefcorals.com
http://www.rrccorals.com
http://www.lumalighting.co.uk Rich Ronson

I’ve noticed this strange phenomenon with bright blue/violet LEDS, my eyes are unable to focus on them in the dark. As these are in the HEV spectrum would it have something to do with it?
http://www.lumalighting.co.uk Rich Ronson

I’ve noticed this strange phenomenon with bright blue/violet LEDS, my eyes are unable to focus on them in the dark. As these are in the HEV spectrum would it have something to do with it?
http://www.lumalighting.co.uk Rich Ronson

I’ve noticed this strange phenomenon with bright blue/violet LEDS, my eyes are unable to focus on them in the dark. As these are in the HEV spectrum would it have something to do with it?

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