[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [APD] Just how accurate do we need lighting recommendations to be?

On 19/09/2005, at 4:47 PM, Jerry Baker wrote with snips here and there:

> David Aiken wrote:
>> I don't think that level of precision is necessary for  that  
>> purpose. The knowledge may be intrinsically useful to you, but   
>> knowing precisely what lighting level you need to maintain the   
>> internodal spacing of a particular plant within certain closely   
>> specified parameters - your example - in a given tank with a given
>> population and maintenance regime is not particularly useful at a   
>> practical level for most people, nor for you when you set up a   
>> different tank. The level of variation and adjustment required on  
>> all  parameters in a different tank than the one which yielded the  
>> answer  is large enough to ensure that a less precise answer is  
>> probably  going to be just as useful in practical terms for most  
>> people.
> Again, I don't understand how you just know that without testing  
> it. I'm not saying it is, or isn't the case. I am saying that you  
> cannot say, "measurement X will have no value because everything  
> else will negate its effects" when you haven't even measured any of  
> those variables or observed their relationship under controlled  
> conditions.

I'm not saying that "measurement X will have no value because  
everything else will negate its effects". I'm suggesting that given  
the range of relevant parameters and the levels of variation in those  
parameters reported in places like this list, plus the fact that many  
tank owners do not routinely test for all individual nutrients and  
many of those who do test for some use commonly available  
colorimetric tests which have nowhere near the degree of precision  
you're suggesting for lighting, using a highly precise lighting  
recommendation obtained in a test where all other parameters are  
precisely known and controlled is not going to give equivalent  
results in the average hobbyist's tank, and the hobbyist is going to  
end up applying the same rules of thumb they apply to get good  
results with much less precise lighting recommendations. I'm also  
suggesting that if that is the case, then the higher degree of  
precision in the lighting recommendation isn't really adding anything  
significantly useful.

And given the fact that lights come in bulbs/tubes with fixed wattage  
and not all bulbs/tubes of the same wattage are equivalent nor are  
all fittings, it's simply not going to be the case that many  
hobbyists are going to be able to provide their tanks with the  
recommended lighting level if it is very precise. There's going to be  
a degree of variation based on bulb/tube and reflector choices plus  
height above the water and that level of variation is going to  
interact with the variations in the other parameters as well.

So I think less precise recommendations accompanied by suggestions  
for how to adjust other parameters if the lighting is at the high or  
the low end of the range is simply a more practical approach.

> Of course it's more than is required. I'm not interested in the  
> status quo ... everyone's doing that. I'm interested in pushing the  
> boundaries. How do you think someone discovered a better way to  
> measure the amount of light useful for photosynthesis? They had to  
> ask themselves why some lights seemed to be working better than  
> others in growing organisms which rely on photosynthesis. They  
> couldn't just "raise or lower" a light over a tank and deduce that,  
> in terms of photosynthesis, light with a wavelength between 400nm -  
> 700nm is fairly equal. That took measurement and control groups.  
> They came up with PAR. Now we have a tool to assist us in further  
> study. One step at a time, new knowledge is built on older knowledge.

That's all true and fine, and it's really useful for those people who  
want to push the state of the art and run their tanks at the bleeding  
edge of the high tech approach. Most people don't. I quite happily  
applaud those who do because they're the ones who are going to  
discover a lot of the knowledge you're searching for - see below for  
some comments on what I know of that is available, and on the  
availability of research info generally.

I'm not saying we should forget about it. Take a look at reef tanks  
where a lot of what was bleeding edge, assemble it yourself  
technology a few years ago is now being marketed in readily available  
commercial devices that are easy to instal and run. The first person  
to try running a moon light on a cycle approximating natural  
moonlight had to write his own computer program to control the light.  
There are now moon light controllers commercially available. No doubt  
we will see that sort of trickle adopted in planted tanks too over  
time, and more precise recommendations will become more and more  
useful as they are more easily implemented but I suspect that a lot  
of it will have to be adapted from reef tanks which is where the  
market appears to be.

But the fact is that a given recommendation on lighting levels that  
is fine for a tank with CO2 and a given level of fertilisation is not  
going to be useful for the person who wants to run a low tech, low  
maintenance tank with a simple fertilisation routine and no CO2.  
People choose to run tanks at different levels of complexity and  
maintenance and it helps if the recommendations are general enough to  
be able to be applied to different situations, and the more general a  
recommendation is, the less precise it will be.

> Perhaps there is a lot of research that I am unaware of. Is there  
> somewhere I can read about internodal spacing its specificity to a  
> particular species? This is exactly the kind of information I'm  
> trying to get. I don't understand where you learned that light  
> levels and its effects on internodal spacing has no bearing on any  
> other aspect of plant appearance. Is this published somewhere  
> publicly accessible?

I've only seen general comments that indicated that internodal  
spacing increases as light intensity increases, if I remember  
correctly, and I can't remember where I saw it. The best book I've  
seen for this kind of information in relation to hobbyist planted  
tanks is Diana Walstad's "Ecology of the Planted Aquarium" but all of  
the information in it tends to be slanted towards her preferred  
approach of low tech tanks with soil substrates and minimal  
fertilisation, and the overall lighting recommendation is 1 to 2  
watts per gallon of tank water and less for shallower tanks or if the  
tank is near a window. I couldn't find anything in it on the  
relationship of light with internodal spacing on a quick look.

Even Adey and Loveland's "Dynamic Aquaria" which has a very technical  
discussion of light intensity in natural systems and uses PAR units  
doesn't give that sort of information and while it does give some  
information on PAR levels from some artificial lighting setups, those  
setups are often models of natural habitats with the lighting 3-4  
feet above exposed soil surfaces, not the sort of average home  
aquarium most of us have. They do talk about recommendations for VHO  
fluorescents in terms of watts per square foot of water surface under  
certain conditions in places, however but there is no precise  
translation of those levels into PAR units and no comment on how it  
affects particular aspects of growth. The emphasis there is on  
replicating natural environments to some degree.

Both those books cite piles of references so you could spend months  
tracking things down, and they are the 2 most scientific/technical  
texts that have some coverage of planted aquariums that I've come  
across. I'd love to find something at a greater depth than Walstad's  
book and more specifically slanted to home size planted tanks than  
"Dynamic Aquaria". The other important point is that most research  
isn't published or mentioned in books - it's published in  
professional journals and you really need access to some of the  
professional publication databases to start tracking things down and  
there's a real art to searching them.

It's also really quite amazing what things get researched and what  
things don't. People tend to research things they think will be  
useful, or which come with funding attached, so it's quite possible  
that no-one has actually researched your or my pet interests. I can  
remember when I was doing a research project for my post graduate  
qualification and I wanted to look at how often computer users should  
have their eyes tested because my employer had an agreement to pay  
for testing of its staff and it obviously made economic sense to test  
no more frequently than was reasonable. A full scale literature  
search produced only one reference with no cited studies to support  
the recommendation given. The study I did ended up supporting the  
recommendation and I subsequently presented that research at a  
conference chaired by one of the authors of the recommendation, a  
professor of optometry. When I spoke to him afterwards and asked  
where he got the data for his recommendation from, he told me that he  
and his co-author had no data and weren't aware of any - they had  
simply discussed the issue and came up with what they thought was a  
good recommendation. My small study may actually have been the first  
attempt to research that question, which I actually found quite  
surprising. I thought it would have been a fairly likely topic for  
there to have been at least some prior studies. If that's the  
situation for research on a health related question, I have a strong  
suspicion that the level of research on some of the questions we  
aquarists have about our tanks is even more challenged.

David Aiken

Aquatic-Plants mailing list
Aquatic-Plants at actwin_com