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Spectrum...doesn't matter...does it?

I don’t think we need to worry too much about the date the paper was published - 1977 (reposted below for convenience), and I am sure that the research was conducted with appropriate scientific rigor. But maybe Tom Barr will be able to vouch for the above since he may have been taught by these guys; he has an MSc in Botany from the same university - University of Florida Gainesville

From what I can gather, the spectral response of different plant species is variable, but in this case the quality of light is important not only to plant morphology but also to the rate of biomass accumulation. The figures in Table 3 are the results from 5 weeks growth and are pretty significant (dry weight is a more reliable method of measuring plant growth than fresh weight).

However, perhaps it usually isn't an issue for us hobbyists because the bulbs we tend to favour probably emit enough light of appropriate wavelengths for photosynthesis to occur at a rate that allows for healthy plant growth. Beyond that I suppose it doesn't matter what bulbs you use, actinic, day light etc.

Note the research also explains why plants are often found to grow well under actinic lighting because its spectrum peaks around 420 nm (blue light), which after red light yields the best growth.

http://www.apms.org/japm/vol15/v15p29.pdf ...Effects of Light Quality on Growth and Chlorophyll Composition in Hydrilla (1977, T.K. Van et al)
 
Troi,
The thing we need to consider is that the tests in that paper were done with the color constraints of white as a reference and then with only red, blue, and green. They used filters which narrowed the transmission to very tight wavelength tolerances, though they do mention that there were some leak-through of other colors. They really had difficulty in isolating the colors and probably we would have seen wider margins of dry weight had they been able to do a better job of separation.

However, the fact remains that no one uses bulbs that are only red or only blue. All the bulbs we use have all colors. They all count as white light, so we will not see the same level of color isolation from bulb to bulb because all the bulbs we use simply have a different mix.

So this is something totally different than comparing Kelvin or comparing the spectrum performance of different bulbs. As I said, do the test yourself with different bulbs and without color filtration, and no matter which bulb you test, you will not see any difference in growth or health.


Cheers,
 
I have to agree with Ceg4048 and Ian to a degree. I believe that the information on the paper is dated and science has probably moved on from that position or at least developed from that position held. The content may be still relevant but as an experiment it is hardly conclusive. However if they had used LED light, then it could potentially be more relevant (if the correct LED colours are used only the colour used is in the spectrum) and I believe there are more papers available that have done this.
One thing I always find personally, is that there is a missing link between the latest scientific knowledge/position and the information available to the general public. There does not appear to be any suitable linking mechanism from one to the other. If this was cracked, then it would allow people to gain more insight and produce more indepth contributions from a topic point of view.
The forum that can make this linking connection, will be the one that will prosper, as it will be able to support information factually, that people can have confidence in. This is not to have a dig at anyone that has done things through reptition of practice. As this is required also. However it allows many other factors to potentially change/creep into the results, or duplicates the ingredients of the contents of the replication in the first instance without knowing it.
However we all have to accept that our knowledge today may not be 100% correct and may alter slightly when other discoveries are being made. Lighting is one of those subjects, I believe, that will be evolving as more is learned and released to the general public. Also do keep in mind that all plants are different, they have variable lighting requirements which supports the theory that, the "correct" lighting may be a variable that is unachievable in a mixed planted tank? This would also support the point that the plants (or aquatic weeds) will adapt to any lighting and environmental conditions available, if they are to survive.
 
Hello,
It's not really clear exactly what you disagree with. It's certainly a fact that none of us know 100% of the real facts. Those of us who have grown plants successfully have come to the realization that it really doesn't matter what type of lighting is used, and that what's more important, by far, is that whatever lighting is used, it's much more important to avoid using too much. None of the fluorescent bulbs have demonstrated any superiority over their rivals. They all contain blue and red, which are consistent with the fundamental frequencies of the chlorophyll response curves. The remaining colors in the spectral characteristics of the bulb are handled by the auxiliary pigments produced by the plants, which transfer their energy to the chlorophyll complex.

There is also no definition of "correct". If you can grow a plant to satisfaction, wherein the plant is healthy, is algae free, has acceptable growth rate and is not suffering any malady, then can this be considered correct? If this can be achieved with a variety of color combinations then why limit one's self to a particular color combination?

Hobbyists gain confidence when they follow the instructions and are later rewarded with success. Folks do not enter the hobby because they want to study the latest science of lighting. They simply want to grow plants trouble free. But the world has too many myths and hobbyists often fall prey to those myths. The biggest myth in planted tank lighting is that 6500K is correct. This is simply not true and that has been demonstrated many times.

With the advent of LED fitted with specific color diodes it may later be shown for example that since color isolation becomes possible, we will be able to reproduce the efforts in that journal article. So, for example, when initially flooding a tank, it may be possible to give the plants a head start by restricting the color to only red. Again, this is something that has to be tested and verified in someones tank, or groups of tanks fitted with LED. If you have actually performed these tests in actual tanks and have results to share then we're definitely interested in seeing those results. We really don't need to be scientists to do these tests. We just have to make sure that the test process is a scientific one.

As it stands now, what we observe in out tanks consistently, is that there is a much greater impact to the health of the plants from application of CO2, nutrient levels and flow distribution and maintenance practices than any effects due to spectrum. The health of the plants and the growth performance is the result of a combination of things that we do. Some factors are more important than others and the effect of any one factor can be mitigated by careful adjustment of the other factors, so really, there is no overriding priority to find "correct" spectrum.

Cheers,
 
Good Morning Ceg4048,
Sorry for the confusion, what I was trying to say, is that I feel my thoughts align currently along the lines of what you and Ian are saying. However the limits are within our current knowledge which may not be 100% of what is factual happening. I have a tendency to be cautious over making statements on my present knowledge, due to the changes in the science and technical discoveries that improve our knowledge on a daily basis, it can sometimes come back and bite me in the bum later.:) ;)
I agree that the world of fishkeeping has many myths and these need to be put to rest quickly and I am sure with sites like this they will.:clap: However I do feel that the lack of connection between sites like this and the scientific communities out there prevent the myths from propagating more quickly into folklore. I agree that teaching newcomers has to be a priority on this site and with a well laid out basic understanding of the facts, it should prevail into common knowledge. However I am sure you will agree, there are many intelligent individuals also present here, that would like to expand their knowledge and understanding through conversation and learning in a more light hearted manner than possibly following laid out instructions.(no matter how good the advice)
I do know there are papers out in the internet that discuss LED lighting experiments. I will be happy to look out for the ones I have read, but i am unsure as to the legalities of reproducing others work on commercial websites? Maybe I could do a review of the information, to bypass it. :bookworm:
The LED experiment has already been done, to some extent and I will try to get a paper to support this claim with the above caveat in mind. I agree there may appear to be no overiding factor to gain the correct spectrum. However there may be an optimum lighting condition, that provides the best results of all the main important mitigating factors. :woot:
Regards
 
Hi,
You can easily link to the paper or quote the information from it as long as the source allows reproduction. If direct reproduction is disallowed then it might be better to simply paraphrase or to summarize as you suggest. Of course we need to know who is doing the experiments so that we can understand if there is possibly a bias.

Cheers,
 
Glad I found this. There's much talk of spectrum the world over as mentioned, and each time someone links to a spectrum, I don't see vast differences (on the whole) between many. I understand spectrums in terms of transmission values, but only for HD cameras.

The LED side of this intrigues me, and looking forward to the references. As a side issue I'm interested why even some manufacturers say that their LEDs are no good for plants - have they been sucked in to the spectrum legend? I'd go LED if long enough units were cheap enough - low running cost, and hopefully less heat in to the tank. Got a 2' tank, love a nice cheap LED clip over unit for it.
 
ceg4048 said:
Troi,
The thing we need to consider is that the tests in that paper were done with the color constraints of white as a reference and then with only red, blue, and green. They used filters which narrowed the transmission to very tight wavelength tolerances, though they do mention that there were some leak-through of other colors. They really had difficulty in isolating the colors and probably we would have seen wider margins of dry weight had they been able to do a better job of separation.

However, the fact remains that no one uses bulbs that are only red or only blue. All the bulbs we use have all colors. They all count as white light, so we will not see the same level of color isolation from bulb to bulb because all the bulbs we use simply have a different mix.

So this is something totally different than comparing Kelvin or comparing the spectrum performance of different bulbs. As I said, do the test yourself with different bulbs and without color filtration, and no matter which bulb you test, you will not see any difference in growth or health.


Cheers,
Click to expand...

Exactly...I think that is what I said...so in that we are in agreeance. The paper provides conclusive evidence that in the case of hydrilla, at least, spectrum does in fact have a significant impact on morphology and growth rate.

Confusion arises because what is often meant when it is said that spectrum output isn't important to plant growth is that there is very little difference between specialist T5 bulbs that manufacturers claim enhance plant growth and the cheaper alternatives...(colour temperature aside, which is a different but related issue).

The two are very different propositions and I think that in future we need to be careful before making potentially misleading statements. In other words the statement "spectrum doesn't matter" needs qualifying, and I think that this has now been done.

But just in case there is any residual confusion, I'll repeat what I stated in my previous post...

...Spectrum does matter to plant growth but it is not necessarily something that we as aquatic plant growers need to worry about because the bulbs we tend to favour probably emit enough light of appropriate wavelengths for photosynthesis to occur at a rate that allows for healthy plant growth.

At the risk of confusing the issue, but with the hope of providing further clarification...This is supported by the increasing use of PAR meters rather that LUX meters. PAR meters allow us to compare or gauge how efficient our chosen lighting is at reproducing the spectral range designated as photosynthetically active radiation (PAR)...the clue is kinda in the title.

In short, if spectrum were not important to plant growth why bother using a PAR meter?
 
bulb manufacturers have been demonstrating the "ideal" wavelength of their "growth type" bulbs all the time. So the peaks in blue and red spectrum sensible to plants mean something or nothing?
 
With reference to my above post yes they do mean something...but perhaps not as much as manufacturers would have us believe in relation to their particular branded bulbs. And in particular since the cheaper alternatives we favour probably emit enough light of appropriate wavelengths (red and blue light) anyway.
 
Manufacturers will make available what is in demand, so if a plants are said to need peaks at x y and z wavelengths, then they're going to supply the demand. If a renowned planting guru stated that this new wavelength worked and this nobrand tube delivered it, Arcadia and all the others would start making a tube to suit.

I think Troi has hit the nail on the head, does spectrum matter in the aquarium generally? I've never looked that closely in to it as I've never been that concerned, I've either run with what the tank came with, or what suited my wallet or eye.
 
Troi,
The issue of peaks is also part of the spectrum argument and it should be addressed. Peaks are irrelevant because they do not tell you anything other than the energy contribution at a specific wavelength. As demonstrated by this very question, spectral curves are not at all understood and that's another reason their relevance is questionable. People don't realize, when assessing the value of the curve that the energy of wavelength groups is dependent on the area under the curve, not the peak value, which is meaningless. There are no plants that "require" peaks anywhere.

Furthermore, it is the area under the curve that is most closely related to PAR, so that's why a PAR meter is relevant.

While manufactures can be said to produce what is in demand, as it turns out, they are the ones telling folks what they should be demanding. We see this every day. And what is in demand when it comes to lighting freshwater tanks is not necessarily what should be in demand. People have not be demanding so-called 6500K bulbs just because they knew anything intrinsically. They were told that they needed it and so they demanded it. An illusion of the highest order.

That is why spectrum is much more a sociological issue than it is a scientific one. The problem is that generally, many do not understand the rudiments of plants and neither do they understand the rudiments of light. That's why I continue to maintain that we need to test for ourselves. We have already seen that the experiments listed in the link had only very limited relevance to us even though the data, results and conclusions seem to suggests otherwise.

One can say that wavelength or frequency matters, but spectrum, by it's very definition (a band of colors), as it applies to a planted tank, does not matter. On the other hand, PAR, regardless of spectrum, matters. PAR determines the rate of growth because it relates specifically to the energy input to a photosynthetic organism, and photosynthesis is, by definition an energy conversion mechanism.

Cheers,
 
I agree...I think - that is if I understand you correctly...in so much as the peaks just demonstrate the effectiveness of different wavelengths of light in driving photosynthesis. That is why the peaks correspond most markedly with the absorption spectrum of chlorophyll a (wavelengths below 500 nm - blue light, and above 600 nm - red light). So in this respect spectrum does matter.

PAR designates the "spectral" range, or if you prefer "wave band", of solar radiation from 400-700 nm that organisms are able to use in the process of photosynthesis. As far as I understand it PAR meters are weighted specifically to tell us whether our plants are receiving enough light of the right quality to promote efficient photosynthesis.

The results of the paper are very relevant to us as aquatic plant growers but its something we need not worry about because on the whole the bulbs we tend to use e.g. full spectrum HO T5s output enough PAR to ensure that our plants grow well and remain healthy. That is also why manufacturers claims regarding special growth type bulbs as opposed to the cheaper alternatives are perhaps more than a little overstated.
 
PAR is much more than a designation of range. Any light in the visible spectrum is usable. PAR is a measurement of the number of photons crossing a unit area per unit time. It is the number of photons that strike a pigment molecule per unit time, combined with the specific energy gain of the electron that determines the effectiveness of the light. It has nothing to do with wave or band because the property of the light that is relevant to photosynthesis is the particle property of light. The particle property determines the number of particle collisions with the chlorophyll's valence electron. The wave property determines the energy inherent in each collision. Light is both particle and wave, and each of these properties are responsible for the reaction with the pigment molecules.

When you see a sharp peak in a spectral graph, this is just a record telling you that there are some photons having a specific energy level present in the storm. But those photons alone do not determine the total number of collisions and the total energy being seen by the leaf. The leaf sees the sum total of all the photon particles at all the wavelengths shown under the curve. The amount of energy delivered by the photons in the peak is very small compared to the total amount. So sharp peaks are meaningless. If the peak broadens out and produces a wider area then that tells you there are more photons of that frequency present in the storm.

I think that is what you are missing. If you review the article you'll see that the only way they could compare the performance of the individual colors was to raise or lower the light so that the PAR for each color was the same. That alone should tell you that PAR is important, because when the PAR values were equalized it means specifically that the same number of photons were crossing over the same amount of area in the same amount of time.

So, they equalized the "photon flux density" to 30 microeinsteins per square meter, per second. That means 1,806,000,000,000,000,000,000 photons (1,806 billion billion) individual particles were crossing over one square meter every second.

When they used the blue filter, about 50% of those particles (903 billion billion) each were vibrating at 1/300,000,000,000 or 3.3 trillion times per second. The other 903 billion billion photons were vibrating at slightly different speeds. That's what the wavelength means. The energy inherent in some particle vibrating at 3 trillion times per second collides with an electron and that particle is annihilated. All the energy that was that vibration is now given to the electron and it is this electron energy that allows it to escape the bond of the chlorophyll to be used in a chemical reaction.

So that's what PAR tells you. It tells you exactly how many possible collisions can occur. You cannot dismiss PAR as some kind of vague "wave band" or "quality" or "promotion". That is a complete misunderstanding of the data.

Here is what's actually relevant about that article. In fact it's so relevant that it is completely mind blowing and nobody is actually paying attention because they are too busy being fixated on vague "wave bands":

Red photons actually have the lowest vibration energy. They have the highest wavelength (680) and thus the lowest vibration frequency. In electromagnetic fields, the higher the frequency, the higher the energy. That's why microwaves and X-rays and Cosmic rays will kill us outright. They have the smallest wavelengths and therefore the highest frequency.

One would expect that blue light, having the higher frequency, and chlorophyll having a higher response to blue should generate the higher growth rate, yet, look at the data, the frequency that generated the highest growth rates is the lowest frequency, the lower response of chlorophyll and the lowest energy level. Think about that for a minute and think about the implications. So the question we should be fixated on is: WHY?

Cheers,
 
Absolutely, any light in the visible spectrum is of course usable since both PAR and the visible spectrum are one and the same, give or take a few nm.

Sure the peaks don't tell the whole story and this is where accessory pigments come in to play and why compared to the peaks in the absorption spectrum for chlorophyll a the peaks in the action spectrum are broader and the valley narrower and not as deep. This was observed by Thomas Engelmann in 1883.

And thanks for your treatise on PAR, but I think that perhaps the issue is becoming unnecessarily complicated. The bottom line is that many of us go to great lengths to ensure no limits to plant growth in our aquariums whether we're discussing fertz dosing, CO2, or indeed as on this occasion artificial lighting.

Whichever way it's spun, put simply, spectrum is important to plant growth. For instance, if deficiencies in the blue and red wavelengths become limiting factors to growth the plant is forced to compensate, maybe through the production of more chlorophyll and accessory pigments. And this is not particularly good news since in the words of the Tropica boys...

'...Adaptation to resource limitation is a costly affair. Whether the plant invests in more chlorophyll or more enzymes it results in higher nutrient requirements and higher energy use. The higher energy use comes from the fact that proteins require constant maintenance in the cell to work properly and these maintenance processes absorb valuable energy and carbohydrates, which might otherwise be used for growth purposes...'
 
Interesting to read the different viewpoints here.

Question is, in the typical aquarium, say 60cm from top to bottom, will any white bulb that has something in the red and blue spectrum near the alleged peaks be able to deliver the required energy through what is basically shallow water? Even with T8 lighting, what will the reduction of intensity be after punching through 2' of water? Might go see if I can find the box for my Interpet Community Daylight tube for my old tank. See what the spectrum was for a non-plant tube.

Colour temperature, IMO is irrelevant, buy the colour you think suits your tank, to a point.
 
Troi said:
For instance, if deficiencies in the blue and red wavelengths become limiting factors to growth the plant is forced to compensate, maybe through the production of more chlorophyll and accessory pigments.
Click to expand...
And so what? When have you ever seen a deficiency in blue or red? This never happens. When people have problems in a tank, virtually 100% of the time the problem is due to having too much blue, red and other colors. I have never seen any deficiency of blue or red photons using any of the bulbs, whether using cheap Tesco or expensive "plant" bulbs.

The quote you lifted applies to all resources, and especially applies to CO2, which is the prime limiter in a tank. When we are solving health issues in a tank, it is actually necessary to intentionally limit the photon flux, because the health issue is usually caused by a resource limitation other than blue or red photons, and the abundance of those photons makes the situation worse. That is a certainty. And if people continue to worry about a resource being limited, when in fact that resource in question is actually in overabundance, then they will continue to have problems, and they will deserve their misery. There is so much more to worry about in a planted tank that it renders spectrum academic. Gas exchange is 10,000X more important to plants because gas diffusion under water is 10,000X slower. Photons do not have any trouble finding their way to the bottom of the tank, so this is never a problem. Plants grow because of gasses. Their growth behavior is only mediated by the characteristics of the photons.

Troi said:
And thanks for your treatise on PAR, but I think that perhaps the issue is becoming unnecessarily complicated.
Click to expand...
I went through great lengths to address a complicated issue in the simplest way I could. If you want to simplify it even further, then just don't worry about it because you will never see a limitation of red and blue when using fluorescent lighting, no matter what bulb or what spectrum you choose. That's what we have been saying all along. If someone wants to use LED and isolate the spectrum to all red or all blue, then good luck to them, but I wouldn't want to spend my viewing time looking at a red tank just because the article shows that red produces a higher mass increase rate than white.

All these arguments about how spectrum is so important are false because no one has ever demonstrated the results of red starvation or of blue starvation in a standard planted tank, using standard lighting. As I mentioned in my first post, the data from these experiments have to be related to be within the context of our tanks. The data is useful and instructive of course, but one cannot find correlation to the system we have in place. You will never see a 70% difference in growth rates in 5 weeks using any of the bulbs we have at our disposal as you saw in the article. In fact, the differences between the bulbs will be imperceptible. That's how different our situation is from theirs. Again, you have to try it and see for yourself, not assume that because the article derives a conclusion then it automatically applies, because you do not know of, and have not accounted for, all the anomalies of the tank compared to their setup. Have you considered for example that plants in the tank will reflect inbound light and will change the local spectrum in their vicinity, that the spectrum profile in a tank is not static and is not equal? Have you considered that the plants response to a color is actually modified by the presence of other colors? This is so complicated, and the gains are so minimal, that it isn't worth worrying about.

Cheers,
 
I got some 8w t5 6500k daylight tubes from a lamp supplier in leeds for £2 each. arcadia tropical daylight are £10+
Im gonna use em now and see what happens cos i wont mind replacing them every 6-8 months and if plants grow without unwanted algae then i wont think twice about using them in another tank
 
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