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Plant ID Help (crypt look-a-like with thick tall stem)

This is a discussion on Plant ID Help (crypt look-a-like with thick tall stem) within the Beginner Planted Aquarium forums, part of the Beginner Freshwater Aquarium category; --> On the light intensity issue, I have very limited scientific knowledge--which is to say basically none--so I won't belabour that. But redchigh's mention of ...

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Plant ID Help (crypt look-a-like with thick tall stem)
Old 12-31-2011, 01:45 PM   #11
 
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On the light intensity issue, I have very limited scientific knowledge--which is to say basically none--so I won't belabour that. But redchigh's mention of Ms. Walstad's scientific findings (or reported findings of others) is significant, and I am convinced the lumens is the issue. When using the same length/wattage tube over planted tanks, and the Life-Glo 6500K produces singificantly better results than the Aqua-Glo, which is half the intensity via lumens, even though producing the wavelength required most by plants, I'm satisfied with that.

If one has enough light intensity over a tank, and provided the necessary red and blue is present, plants will grow though in varying degrees. But the trouble is that algae may take advantage of so much weaker light. Plus the colour hue that I find distasteful but that is simply a personal preference. The light intensity is the significant issue; and I see no reason to use double the energy with the weaker tubes, costing more money, and risking algae and less productive plant growth. If that makes any sense.

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Old 12-31-2011, 03:58 PM   #12
 
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Don't sell yourself short, Byron, you obviously know quite a lot. I hope I didn't come across as being argumentative or a know-it-all, I'll freely admit if my assertions are proven wrong (though I'm not yet convinced the experiment cited has done this).

Also, I agree that for aquarium usage, a full spectrum bulb of around 6500K is one of the best choices (there are, of course personal preferences, as Byron mentioned). It is a good balance between bright, white light and photosynthetic supporting light. So with that in mind, some of what I referenced may be more relevant to a discussion of indoor, hydroponic gardening where the only concern is the yield of tomatoes, but here we also want a nice display, which generally means a more balanced spectral output like that from a 6500K bulb.


However, I do find the topic interesting and it could be useful in certain circumstances, such as when trying to maximize plant growth when using a lower wattage fixture or when trying to minimize photosynthetic potential to avoid algae when using a high watt unit. Bulb choice in either case could mean the difference between buying a new bulb or buying a new fixture.


On the issue of intensity (specifically lumens/lux), I will just ask: From whose perspective? Ours? The plants? What about from a honeybee or a pit viper? Would the bulb's respective intensity be retained when perceived by the different organisms?
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Old 12-31-2011, 04:32 PM   #13
 
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Quote:
On the issue of intensity (specifically lumens/lux), I will just ask: From whose perspective? Ours? The plants? What about from a honeybee or a pit viper? Would the bulb's respective intensity be retained when perceived by the different organisms?
The light colour spectrum may make it appear more or less "bright" to us and various animals, but the actual intensity whatever the spectrum can be measured in lumens. I have had discussions with various authorities on planted tank forums about this, and my understanding is that the lumen rating is the intensity of the light. This can be measured with instruments. This intensity is what depreciates so quickly as fluorescent tubes burn, and as it does so the plants have more and more difficulty managing. I cannot see this occurring, though when I replace an old tube after 12 months with a new, the tank does appear a tad brighter even to me. But more significantly, this decreases the algae and increases plant growth, always.

Diana Walstad in her book, and on her forum, advocates a colour spectrum between 5000K and 7000K and/or a CRI [Colour Rendering Index for those not familiar with the term] between 80 and 100. She says that she will use any tube that has either of these ranges, depending whichever is given for the particular tube.
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Old 12-31-2011, 05:05 PM   #14
 
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This is where we disagree. I contend that luminous power (lumen) is only relevant when considering light as perceived by human beings. It is a weighted scale adjusted according to the variable sensitivity (see luminosity function) of the human eye.

Radiant flux (watts) is a measure of total light output without regard to sensory perception.

Last edited by Quantum; 12-31-2011 at 05:07 PM.. Reason: better grammar
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Old 12-31-2011, 06:05 PM   #15
 
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Originally Posted by Quantum View Post
This is where we disagree. I contend that luminous power (lumen) is only relevant when considering light as perceived by human beings. It is a weighted scale adjusted according to the variable sensitivity (see luminosity function) of the human eye.

Radiant flux (watts) is a measure of total light output without regard to sensory perception.
Watts is only the measurement of energy used by the tube/bulb to produce the light. It has absolutely no direct relation with intensity. Only when comparing identical tubes/bulbs can watts be a guide to intensity, as for instance a 10w CFL GE daylight bulb will be less intense than a 13w CFL GE daylight bulb. But both of these might be much more intense light than a 40w bulb of some other manufacturer and type. This is why watts per gallon is so meaningless today, we have such a variety of different types of tubes/bulbs, and the intensity is dependent upon the phosphors (in tubes) that are used. Now that i think of it, that may have something to do with the colour.

I said i wasn't scientifically knowledgeable on this, and I did mean that honestly. There are writers who have said differently, but in my discussions elsewhere I have been told that lumens is a useful measurement of the intensity of a tube. Which makes sense. After all, regardless of what I may perceive, the intensity of 10 burning candles compared to 1 or 2 candles is higher, and this is all that lumens is measuring.
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Old 12-31-2011, 10:38 PM   #16
 
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I have been scouring the web most of the day (stuck at home with step throat on new years eve, yay me) and I for the life of me can not find the lumens for the Aqueon 8000k bulb. Do either of you (or anyone else) know the actual specs on this bulb? So far plant growth has been moderate in the tank, but it is very clearly "dimmer" than the 10g with the CFL. I can stand in the hallway and see both at the same time and it is a major difference. I'm just trying to absorb some of the knowledge from your discussion :)
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Old 01-01-2012, 10:39 AM   #17
 
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I agree with what you've said about watts as far as the electrical energy input, but will add that it is not the only application of the term in the context of the conversation. Radiant flux, the total electromagnetic energy (light) emitted can also measured in watts. So watts for input and watts for output. The output here meaning the release of energy as photons, which can be quantified as watts (energy per unit time).

The candle example is a bit of a false analogy; yes, assuming all the bulbs are the same, the light of ten bulbs (or a single bulb of 10X the wattage) would have a higher lumen count than that of one. But aren't we comparing two bulbs of the same wattage? A better example would be burning two chemicals, one creates a green flame and the other blue. The amounts of each have been calculated so that they emit the same amount of light energy. This would illustrate how two light sources of equal energy would have different lumen counts.

Before I continue, I should say that I have no specific training in this field either, just a knowledge of the basic principles from a natural science background. The rest I've tried to learn on my own, to which this conversation is contributing. Also, I want to make sure we are on the same page regarding terminology. To this point, I have assumed that your assertions are: 1) 'intensity' means 'light energy emitted' 2) a lumen count is a measure of that light energy, and 3) how 'bright' we perceive a bulb to be is indicative of its energy output/lumen count and this is determinative of rates of photosynthesis.

I agree that perceived brightness is proportional to lumen count (everything else equal, the higher lumen bulb will appear brighter), but I contend this is only somewhat related to energy output and not relevant to plant growth. Luminous flux is specifically weighted according to the sensitivity of the human eye (which varies over the visible light spectrum), and since human perception of light and the absorption spectrum of chlorophyll are so different (nearly antithetical), I argue that lumen count/perceived brightness is not a reliable measure or indicator of a bulb's ability to support or drive photosynthesis.

Last edited by Quantum; 01-01-2012 at 10:42 AM.. Reason: removed quotes - didn't work right
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Old 01-01-2012, 11:43 AM   #18
 
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note: the third of the 'assertions' in my previous post should only read energy output and not include lumen count

The 'dimmer' part is what I'm trying to work out, though in your case it would be difficult to compare because of the different bulb types and wattages, as alluded to by Byron.

The only thing I could find regarding the bulb was the spectral graph (from the Aqueon website).


This may all be largely irrelevant, but just to wrap this up, I'll try use this to explain my point of view regarding lumens.

First the luminosity function graph (graphic from absoluteastronomy.com – one of the sites I've used as a reference when trying to figure this stuff out).




This shows the sensitivity of the human eye to the various wavelengths; x-axis is the visible light portion of the electromagnetic spectrum, numbers are wavelengths in nanometers. Looking at the black line, which is for normal daylight (green line is for low light conditions), max sensitivity is around 555nm and tapers off rapidly toward blue and red. I concede here that I may be misinterpreting 'sensitivity', but I take it to mean that it takes fewer photons at 555 nm to produce a response (the perception of it) than those at shorter or longer wavelength.

When calculating luminous flux (which is what is measured in lumens), first the amount of energy of each wavelength is calculated (in joules). It is then weighted according to the luminosity function curve to arrive at the corresponding number of lumen. This number for each wavelength is then added together to get the total lumen count. Not sure how to represent this mathematically, but the idea is that one joule of green light energy counts for more lumens than one joule of either blue or red light energy.

Now this is how I interpret this and maybe it is another spot where I've gone of the tracks if I have. It may be that I have come to the wrong conclusion as to exactly how the luminosity function is used to tabulate lumens. Either way it won't change the fact that luminous flux is specific to human eyesight.

Now for photosynthesis. Below is the absorption spectrum for chlorophyll.



Obviously, very little green is used at all, mostly blue and red. A graph showing the actual rate of photosynthesis vs wavelength is not so peaky and has a broader, less steep curve, but still shows a significant valley at the green section of the spectrum.

So, in this context consider this hypothetical: two bulbs of equal light energy output, the only difference is that one produces only 555nm light, and the other emits 50% 420nm and 50% 670nm. So wouldn't the first bulb have a much higher lumen count (appear brighter), but be essentially useless for plant growth. Conversely, wouldn't the second one be much better at driving photosynthesis while having a very low lumen count (dimmer)? If we put these two hypothetical bulbs on either end of a spectrum, isn't it logical to conclude that we can estimate an actual bulb's performance based on which of the two extremes its spectral graph more closely matches? For example, the Aqueon shown above toward the low lumen/high photosynthesis end and the Hagen Life-glo (below) toward the high lumen/low photosynthesis end.


Last edited by Quantum; 01-01-2012 at 11:44 AM.. Reason: not doing the quotes right - removed the quote
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Old 01-01-2012, 12:40 PM   #19
 
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Amplitude. Up to this point I've only been considering wavelength and not amplitude, still reading.
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Old 01-01-2012, 01:16 PM   #20
 
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I tracked down one article wherein lumens is used as a basis for the intensity of aquarium lighting. It is by Karen Randall, an authority in the area of planted tanks who is highly acknowledged by all of us. She clearly considers lumens the guide to intensity. This article appears on a forum, so to avoid linking the forum I will cut and paste the relevant paragraphs. Everything that follows in this post is from Ms. Randall.

The best place to start is by considering the following parameters that are important when choosing lights for a planted tank.
  1. Intensity of light is more important than spectrum.
  2. Aquatic plants use light in the red and blue areas of the spectrum most efficiently. They are less efficient at using green and yellow light, but they are also capable of using even this part of the spectrum as long as the intensity is adequate.
  3. Red light encourages long, leggy growth, while blue light encourages compact, bushy growth.
  4. Algae is much better at using poor-quality light than higher plants are, so strong light in the wrong spectrum can encourage algae problems, particularly in a tank with nutrient imbalances of one sort or another.
I look for several things in a fluorescent tube for a planted tank. High lumen rating, full spectrum, a color temperature of between 5000 and 6500 K, a color rendering index (CRI) as high as possible and low cost. Very few tubes measure up in all areas.

Remember that the Kelvin rating does not indicate spectral distribution. It indicates the color of the light that a particular tube will appear to exhibit to the human eye. It has more to do with eye appeal than plant growth. Tubes between 5000 and 6500 K come the closest to natural midday sunlight. Ask to see a spectral distribution chart for any new tube you are considering. It should be shaped like an "M," with a spike around 5000 K. If the middle of the "M" is shallow, it means they are filling in with light that humans find most attractive. That's okay, but you want to make sure that both the red and blue parts of the spectrum are well represented, because these are the areas most needed for plant growth.

Next look at lumen output, as well as the drop off over the life of the tube. This is where there is often a big difference between cheaper tubes and more expensive ones. Only you can decide if you'll save money by changing the tubes less often.

There is a new type of fluorescent lighting that has great potential for use in planted tanks. In fact, before too long, these lights will become the standard as higher energy efficiency requirements are imposed on the industry. These are energy-efficient T-8 tubes run on electronic ballasts. They are made with the same rare earth phosphors used in the best full-spectrum T-12 (normal) tubes.

I have been using only energy-efficient T-8 tubes for several years now. Here is a comparison between these lights and a standard 4-foot, two tube shop light (in both cases I am talking about a 5000 K, full-spectrum tube with a spectral curve similar to a Vitalite):

A standard shop light with two tubes uses 94 watts (40 watts for each tube and 14 for the ballast). It produces 5000 lumens. Each tube (assuming Vitalites, one of the least expensive full-spectrum tubes) costs at least $13, and tubes fall off to about one-half the rated lumens by the one year mark.

A two-tube fixture (using GE's SPX 50 T-8 tubes with an electronic ballast) runs at 60 watts (32 watts per tube and the ballast runs at 95 percent, which accounts for the additional 4 watts). It produces 6000 lumens. Each tube costs under $10. These tubes drop about 5 percent in lumens in the first 100 hours of operation, but the rated lumens are after that period. The drop off over the remaining life of the tube (average failure time is 20,000 hours) is only to about 80 percent.
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