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

[David Aiken <daiken at iprimus_com.au>]

On 19/09/2005, at 1:40 PM, Jerry Baker wrote:

> Thomas Barr wrote:
>
>> I never discounted a controlled study, I've done them on lights  
>> and can suggest a very easy and simple way to do this(see above),  
>> not with 600-2000$ or more light meters.
>>
>
> Without light meters, the study isn't of much use to anyone. How  
> are you proposing to quantify the results of such a study so that  
> the results can be applied to arbitrary bulbs and setups? If you do  
> this study using a light kit from AH Supply, how will this  
> knowledge correlate with ODNO setups, or MH? You can't do it  
> without measuring. Measuring is the basis of all empirical  
> knowledge, and without measurement there is no real way to apply  
> the knowledge to a new and unique situation.
>
> <snip>

Sorry, but measurement is not the basis of all empirical knowledge.  
There are all sorts of things we know empirically which don't rely on  
measurement - the sun will rise tomorrow, sugar tastes sweeter than  
salt, your partner's favourite food treat, and so on. There's a huge  
amount of empirical knowledge that doesn't rely on measurement and  
the first humans certainly learnt enough to live and survive without  
any measuring devices.

That's not to say that measurement isn't useful in many areas and  
absolutely essential in some. That's just saying that your claim  
about measurement's role in empirical knowledge is wrong.

So, let's say we pin the lighting levels down exactly. Let's say you  
do what you said you want to be able to do and work out what light  
levels will keep certain internodal lengths under 50 mm, or certain  
plant heights under x mm. You've done your controlled test in  
particular systems with or without CO2, a given fish population, and  
a certain feeding and fertilisation routine. I run a different tank  
with a different fish load, both in numbers, species and size. I use  
a different substrate for whatever my reason of choice is.  
Temperature of the tank is slightly different to satisfy my different  
fish choice. I feed differently and I dose different fertilisers  
because I live in Australia and a lot of your US products and the  
European products available to you aren't available here. You give me  
your data on what level of light I need to get those plant growth  
results.  Now tell me how I apply that data to my different and  
unique situation. There are no rules for doing that other than the  
general rules of thumb we already have for juggling plant growth by  
playing around with lighting and nutrient levels. Specifying light  
levels more precisely for one set of conditions doesn't really make  
it any easier to apply that data in another situation, especially if  
what we're after is the same tightly specified result.

Pinning down necessary illumination levels for a particular result to  
a precise measured level in PAR units, or lumens, in one situation  
won't really help me get all that closer to getting those results in  
a different situation because there's enough variation in other  
parameters in my situation for that level of precision in light  
measurement to be valueless. Across a range of systems and  
maintenance approaches, watts per gallon or lumens per gallon have  
proven to be close enough guides since everything else is going to  
have to be fine tuned slightly anyway.

And when it comes to reproducing lighting levels that accurately,  
just how do we do it? There will be a bit of variation in different  
bulbs of the same brand/model, plus different reflector housings will  
have an influence. Not everyone prefers the same x watt bulb and  
different bulbs will vary from the bulb you used for your tests. Yes,  
we can adjust the light levels in the tank by raising or lowering the  
light fitting but not everyone wants a suspended fitting. Even if  
someone gets a light fitting that can be height adjusted, they are  
then going to have to buy a reliable and accurate light meter that  
measures in the appropriate units and be prepared to use if if they  
are going to end up applying the same illumination levels. The fact  
of the matter is that reproducing a very tightly specified  
illumination level isn't necessarily particularly easy or simple and  
most simply people aren't going to bother trying to do that. If  
you're going to specify levels +/- a certain degree of tolerance,  
then how much tolerance do you allow before we're back at close to  
the same level of tolerance as various watt per gallon  
recommendations have inbuilt in them?

I'm not saying that measurement and research is useless or  
irrelevant. It is extremely useful and valuable, and the more we have  
the better. But a lot of knowledge isn't useful and valuable because  
it can be precisely applied to a given situation - it's useful and  
valuable because it allows us to understand what happens when we play  
with a particular parameter. I think knowledge of lighting levels is  
like that. What we do is get the lighting level into a particular  
'ball park' area and then fine tune the other parameters we can play  
with, or we find that we're not happy with the results we getting and  
we play with the light a bit by changing bulbs or distance above the  
water, or a new reflector while keeping the other parameters  
relatively constant.

What we don't do is precisely and consistently deliver tightly  
specified quantities of illumination, nutrients and whatever else to  
a precisely specified tank size with a precisely specified fish  and  
plant load. We're not necessarily concerned about keeping internodal  
distances under x mm or a particular plant height under y mm - a few  
mm over x or y probably isn't an issue for us. What is too long or  
too short an internodal distance, or too tall a plant, is more often  
an aesthetic issue which we appraise by eye rather than something we  
want to assess in conformity with a measurement. Everyone would end  
up with pretty much exactly the same tank if we all tried to run our  
tanks at that level of precision and aimed for results specified  by  
measurement, and everyone would be unhappy. There'd be nothing  
personal or interesting about this hobby if we did it that way. I  
simply don't think we need that level of precision to get good  
results and I also don't think that level of precision would  
guarantee that our results would be significantly better than they  
currently are, either.

And all of the above is not an argument against doing the research.  
It just represents my reasoning for believing that the kind of level  
of precision you're talking about isn't particularly useful to me or  
to many others at the practical level of running our tanks. We don't  
need things quite that precise at the practical level.

Do the research and publish the results and we all will learn  
something, and it will certainly be valuable to some people. But at  
the same time have a serious rethink about just why you want to do  
that research and just what uses the results will be. I think if you  
do the rethink and work out what you really want to achieve in terms  
that are general enough to be widely useful (internodal spacing of x  
mm for y plant isn't quite general enough to be really useful in my  
view), you'll end up doing the research slightly differently and be  
more interested in determining a lighting range rather than a  
precisely specified lighting level, and discovering how different  
nutrient and other factors influence which end of the range you come  
up with is going to be more beneficial in practice.

That's not a personal attack and please don't take it that way, but  
I  normally lurk and rarely post, and I've been following this thread  
with interest and a bit of amusement and frustration because it has  
seemed to me that there are 3 problems/issues with wanting to specify  
lighting levels so precisely and no-one seems to have really tried to  
pin them all down. Those 3 problems I see are first, the increasing  
difficulty of replicating a given lighting level exactly as the  
specification becomes tighter; second, it really isn't clear to me  
that such precision makes it any easier to get it right in a  
particular system when there's as wide a variation across systems as  
there is; and third is simply my view that the desire for such  
precision seems to be driven by an overly precise and unrealistic  
view of what would constitute a good result in a given tank.

And the real trigger for me in your post was your claim about  
measurement and empirical knowledge. I really couldn't let that one  
go past - it simply pressed one of my buttons, and that's my problem  
rather than yours. Your problem is being forced to read a post as  
long as this  :-)

David Aiken
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