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

[Jerry Baker <jerry at bakerweb_biz>]

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

And how do you propose to define when tomorrow is without measurements? 
You can't define it as when the sun comes up because then you would have 
  a logical absurdity ... that the sun will rise when the sun rises. You 
would probably say, "the sun will rise in about 9 hours."

> sugar tastes sweeter than  
> salt,

That's a measurement. Just because you didn't use a ruler to get the 
measurement doesn't mean it isn't one. If you compared a plant and a 
tree, you would probably say the tree is bigger. Your senses are 
perfectly capable of measurements. In fact, all measuring devices do is 
allow us to increase the resolution of our senses.

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.

You don't need a measuring device to make measurements. Devices just 
aide our senses where we do not have the ability to resolve the detail 
we seek. You do not need a ruler to see that a tree is taller than 
grass, but you probably need a ruler to see that US letter-sized paper 
is slightly wider than A4 without holding them next to each other.

> 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.

No, it isn't. I think you are just thinking of measurements as always 
being conducted with a device.

> 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.

My whole point is that you cannot definitively say which variables 
matter and which don't unless you do the study. I am truly surprised at 
how much resistance there is to this idea. Maybe it is true that there 
are too many variables to account for, but it's also possible that none 
of those variables you listed have any measurable effect. Have you 
tested that? If not, why postulate otherwise?

> 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  :-)

That scares me. I can't tell if you have "art school syndrome" or if 
it's something else. If you don't know, art school syndrome is a 
somewhat common affliction where there is a pathological opposition to 
the idea that something beautiful can be explained, or quantified.

-- 
Jerry Baker
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