Spectrum vs. PAR

[Unarce]

I'm re-posting this because of the non-specific Subject Title I previously listed it under. Hopefully, I'll get some responses this time around.

After tons of research, it seems apparent to me that the spectrum of higher Kelvin ratings would benefit SPS corals more than the high PAR, high intensity lower Kelvin ratings.

I know a lot of hobbyists insist that 6500K is best for SPS to thrive and grow because it's similar to the Kelvin rating of the sun, but I don't see how that's scientifically possible. Unless, you're utilizing an incredible amount of watts in that spectrum along with supplementation to achieve what you could with less watts at a higher Kelvin. It is known that most of our SPS corals originated or were propagated from reefs at around 50 feet of depth. After only a couple of meters, the water becomes considerably bluer with the majority of the higher wavelengths being quickly absorbed, which is what a 6500K bulb mostly consists of.

Since lighting is primarily for photosynthesis, than why would we need so much of the orange, green, and yellow wavelengths:

http://www.reefs.org/library/talklog/s_ ... /acpPC.jpg
http://www.reefs.org/library/talklog/s_ ... 02/pas.jpg

It also wouldn't make sense to try and match the midday sun in our tanks since in nature, it only occurs for a short period of the day and actually has a negative effect on photosynthesis:

http://www.science.uts.edu.au/des/Staff ... hesis.html

There are a million charts showcasing what produces the highest PAR, but can anyone show me any hard evidence as to why a higher PAR is better for corals.

 

[taikonaut]

This is a very complicated issue, and I don't think I have the credential and time to address it... but anyway, here I am.

One thing that you failed to address is that the relative spectral intensity of the different bulbs (hi and low K bulbs). If you superimpose them together, you will notice that the low K bulb (6500K) has higher intensity in almost all part of the spectrum. This is why blue filter can be used on the 6500K bulb to get better performance than a 20kK bulb.

Another issue that you need to consider is the relationship between measurement of ETR and photosynethsis. It is a very difficult experiment, and the link you provide does not give me any setup info. other than a picture of a transducer they used (not explicitly). You really need to be familiar with the field to know if they are slightly misleading in the diagram (general shape I agree with, but the intensity at which the ETR peaks is very questionable.) I suggest you take a look at some reference on ETR, and the web and the following can be useful, albeit a bit old (Li Y.S., Derivation of an electron-transport rate equation, energy-conservation equations and a luminescence-flux equation of algal and plant photosynthesis. Biochem J. 1978 Aug 15;174(2):569-77.)

Another issue is appearance. In addition to the health and growth of the coral, reefkeeper also concern about the appearance of the display. This is why some of us use higher K bulb although we knew our coral can do better with a lower K bulb.

 

[taikonaut]

Alright, here is a diagram from another researcherin au:

I suggest you go to the link and read about the issue in ETR instrumentation as well as compare the curve shape of various authors (it seems that everyone use a different unit for the intensity... a real pain).

 

[Unarce]

taikonaut,

Thanks for taking the time to respond.

I'm sure most would understand that there's a range of spectral intensity among different bulbs. Of course a 400W 6500K might have a higher intensity through the whole spectrum compared to a 175W 10K or 20K bulb, but it wouldn't have nearly the same amount in the photosynthetic spectrum of a 400W 20K.

You're diagram is also from the same researcher of one of the links I listed and really only shows the variations in measuring ETR with different sized probes in certain parts of the coral.

http://www.science.uts.edu.au/des/Staff ... polyp.html

I agree that the bluer look might be more appealing aesthetically, but I'd like to look beyond that. I also once believed that a lower Kelvin was the only way to go, but I needed to find out why before I purchased a new system. It seemed clear that I didn't need to have 400W of 6500K for SPS corals, and spend more on so many feet of actinic supplementation.

We're force-fed information regarding the importance of intensity when there's no facts to backup why. Hopefully, someone out there can give me scientific reasoning as to why.

Thanks, again.

 

[taikonaut]

>... You're diagram is also from the same researcher of one of the links I listed ...

Um... small world...

>... Of course a 400W 6500K might have a higher intensity through the whole spectrum compared to a 175W 10K or 20K bulb, but it wouldn't have nearly the same amount in the photosynthetic spectrum of a 400W 20K.

I was refering to the same wattage, so your statement contradicts my opinion.

I can tell you from experience that there is little, if any, more coral growth from using two 400W MH over a 60 gal tank vs. one with only one 400 watt. Double the light does not equal to double the growth rate, when you are at the higher intensity range. Maybe it is one example why some coral do very well in lower intensity lighting. Keep in mind tha some corals do not do well when too much light is used, such as some mushrooms and softies.

Again, this is a very complicated issue, since besides light, other factors such as calcium, CO2, O2 and nutrients (food etc.) also plays an important part. Intensity and spectrum is only one of the many factors.

 

[Unarce]

Agreed. Lighting is just a part of it.

 

[Unarce]

I'm a bit disappointed.

I know there are a lot of Iwasaki users out there that swear 6500K is the only way to get maximum growth out of SPS corals.

Not one of you can provide any facts as to why?

 

[taikonaut]

>... Not one of you can provide any facts as to why?

As I mentioned above, if you superimpose the output of a 6500K over 20K MH (both 400W), you will see pretty much higher output in almost all the wavelength throughout the visible spectrum. Do I need to be more explicit?

 

[Unarce]

Unfortunately, that proves nothing towards the importance of PAR.

Sure, there's higher output in ALMOST ALL the wavelength throughout the visible spectrum of a 6500K bulb, but not in nearly as much in the useful spectrum for photosynthesis compared to a 20K bulb.

A majority of the output (roughly 60%) of a 6500K bulb is almost useless to corals. That's why photosynthesis among corals is at a stand still during the midday sun.

 

[taikonaut]

>... A majority of the output (roughly 60%) of a 6500K bulb is almost useless to corals. That's why photosynthesis amond corals is at a stand still during the midday sun.

I don't follow your reasoning here.

 

[Unarce]

Reasons were explained in the first post, and evident by the links provided.

Simply put, 60% of a 6500K bulb is in the yellow, orange, and green spectrum which has minimal effect on photosynthesis amongst coral. Roughly 28% goes to the red and blue spectrum which provides the highest peak for photosynthesis.

A 20K bulb puts out nearly 50% in the red and blue spectrum.

 

[taikonaut]

But is that 28% more intense than 50% put out by the 20kK?

 

[MiNdErAsR]

We're force-fed information regarding the importance of intensity when there's no facts to backup why. Hopefully, someone out there can give me scientific reasoning as to why.

Some quotes from an article by Richard Harker (Shedding Light On The Reef )

Speaking of sunlight on a natural reef...
From total darkness, it only takes a few minutes for light to reach levels normally found in a reef tank. Measuring light over a shallow reef off Sulawesi, Indonesia, I found that intensity reached 200 microEinsteins per square meter per second (µE/m2/sec) by 6:30 a.m. This is a light intensity level that exceeds that found on many reef tanks. By 8:00 a.m. light intensity exceeded the intensity found over a tank lighted by 400-watt metal halide bulbs.

He goes on to say...
As the sun rises, light intensity increases more or less linearly until noontime, where it reaches over 2000 µE/m2/sec on a day without clouds (see Figure 1). This level of intensity is virtually impossible to recreate in a captive system with lighting commonly available to the hobby. A 400-watt metal halide bulb generates 2000 µE/m2/sec within a few inches of the envelope.

and finally....
Many hobbyists believe that light at the depth most corals grow is blue. In my opinion, this misguided belief has fueled the demand for high color temperature “blue” metal halide and fluorescent lighting for reef tanks. Water is blue and photographs of coral reefs often feature wide expanses of deep blue water, but other colors are present at depth.

This may or may not answer your question(s), but the article is an interesting read none the less.

 

[Unarce]

taikonaut,

Although the chart isn't all that great to look at, it shows that even a second-rate Coralife bulb provides more light in the useful spectrum than the other lower Kelvin bulbs.

http://www.animalnetwork.com/fish2/aqfm ... f1fig2.asp

MiNdErAsR,

Thanks for joining into the fray.

I found Harker's article interesting, as again like most other articles, focuses on intensity. It speaks of the 2000 µE/m2/sec in midday sun that we cannot possibly duplicate with artificial lighting. Although yes, it does occur naturally but provides no benefit to SPS corals according to the research in the links I provided earlier. Photosynthesis in corals cease during the brightest part of the day. He also failed to mention that most of the day, the sun will hit a particular area at an angle where the light goes through more filtering by the water. It's during these times that SPS corals and clams would receive the most energy.

Although I agree that traces of the whole spectrum can reach corals at greater depths, I don't think it's coincidence that seawater filters out more of what corals don't need for energy, and lets in more of the blue that is most conducive to photosynthesis.

 

[Anonymous]

Perusing this thread, it seems that a misunderstanding between the utility and meaning of color temperature (as measured in Kelvin), or trueness in regards to spectral peaks in particular wavelengths to sunlight is being confused with intensity (brightness of light, measured in lux or lumens).

5,000K - 6,200/6,500K is generally accepted as being "right" in the peaks that mimic sunlight, but this does not speak to intensity or brightness of light. Or.. does it? These peaks can be duplicated quite well, and it is this duplication of something very easily measurable - sunlight - that one endeavors to achieve for their photosynthetic specimens. However, the articles speak more to lacking intensity because it is that which we cannot hope to duplicate (well, not without a small nuclear reactor, at least), and this is actually the problem with visible light and matching the needs of specimens. A large part of this issue arises because the intensity of the bulbs we are able to create cannot hope to be sufficient to penetrate very deeply into the water column as natural sunlight can.

However, as to coincidence of seawater filtering out just the right kind of light that corals need, you've got it quite backwards, mate. The corals have evolved to take what they can get, that is to say that the seawater, previous to existence of corals, has always provided a particular spectrum at particular depths, it didn't change to adapt to the needs of corals, make sense? So, it isn't that they receive more energy, it is actually the case that they cannot utilize said energy during this brightest part of the day (a bit like a tanning response - too intense in the non-visible wavelengths, ultraviolet range - means burning, cell degradation, so on and so forth). The sunlight, therefore, is filtered through a deeper layer overall of atmosphere, but ALSO through a deeper layer of UV filtering ozone. The light intensity difference experienced later in the day happens not because it's got more water to pass through, but because it's got more atmosphere to pass through (the water didn't get deeper.. did it?).

Also, while blue (actinic, for instance, of 420nm) is the most powerful wavelength of visible light for penetration of our atmosphere and water, doesn't mean it's what's used for photosynthesis. This...

lthough I agree that traces of the whole spectrum can reach corals at greater depths, I don't think it's coincidence that seawater filters out more of what corals don't need for energy, and lets in more of the blue that is most conducive to photosynthesis.

... is a clear demonstration of the common misunderstanding made by hobbyists, as expressed in the following statement made by Harker (as quoted above)...

Many hobbyists believe that light at the depth most corals grow is blue. In my opinion, this misguided belief has fueled the demand for high color temperature "blue" metal halide and fluorescent lighting for reef tanks. Water is blue and photographs of coral reefs often feature wide expanses of deep blue water, but other colors are present at depth.

 

[Anonymous]

A search of Advanced Aquarist netted this.

Another "view", or way to consider PAR here - with a good glossary and list of acronyms. While meant to be specific to leaf canopy measurements, it ultimately measures the very same resource we're talking about here - sunlight.

Another link, this time studying sunlight in regards to greenhouse utility.

This one speaks specifically to phytoplankton and measuring sunlight.

PAR conversions and conversations.

 

[greenman]

reefnutz,

I’m not sure if you’re trying to justify to yourself that a higher Kelvin light is better or what......


What they are saying above is plan and simple.....


Even though the 65k is putting out more light in the spectrums you don't need or want. It’s still putting out more light in the spectrums that you do need more then any other bulb.....
Put simply you can change the color of a bulb with all the colors of the spectrum. So if you have a dim bulb with all blue it stills a dim bulb.


Now if you have a bright ass BULB and it’s even in all the spectrums It still has more blue then the other bulb your eye doesn’t see it.


Bottom Line when lighting any tank is what’s going under the lights and what colors can you use that both suit you and the live stock!!!!

And when it comes to more light you all know what bulb that is.

 

[Unarce]

Thanks again guys for contributing your ideas.

It's still all really assumptions with little scientific backing.

seamaiden,

I always appreciate your input and thanks for pointing it out as I didn't mean to imply that the ocean water adapted to corals.

There is proof however that the blue and red spectrum generates the highest peak of photosynthesis in corals.

I will take time later to go over the links you provided. I need to address a pyramid snail outbreak in my tank, right now. Ugh!

greenman,

Untrue. I did post a link that shows that the 20K bulb shows more output in the blue spectrum. More of what the corals need.

The other drawback that I noticed is that the lower Kelvin bulbs generate more heat. Fueling the need for chillers and fans.

 

[MiNdErAsR]

Reefnutz,
I'm kind of confused as to where all this is going. Are you trying to say that if one provides a specific spectrum then it doesn't matter what the intensity (wattage?) of the bulb may be?

If stimulating photosynthesis is the desired goal, then shouldn't maximum PAR be our primary objective? If a bulb with a spectrum lower than 20,000k produces the most PAR, then shouldn't that be the bulb of choice?

 

[Unarce]

I would agree that the wattage of the bulb would matter. We've stuck to the idea that the bulbs are of the same wattage throughout. It just seems that a higher PAR does not translate into better lighting for corals.

Stimulating photosynthesis should be the primary goal for reef lighting, and if you read the research links I provided, you'll see that it points to spectrum rather than PAR for maximum energy.