Re: [APD] watt/gallon rule

[Jerry Baker <jerry at bakerweb_biz>]

Thomas Barr wrote:
> Why do we need to do this ? Why/how does the w/gal rule not work?
> Basic questions might seem too obvious, but I ask them anyway. 

This comment tells me that there is a breakdown in communication 
somewhere. I am not saying that there is something "wrong" with the 
watts per gallon rule, nor am I saying that I have all the data I wish 
to obtain (like the minimum light levels you suggested I should have 
values for before I make any measurements). What I am saying is, how do 
you know for certain that the watts per gallon rule is the best rule of 
thumb in terms of accuracy? Did somebody do some measurements and 
determine that lumens per gallon, PAR per gallon, lumens per square 
inch, or PAR per square inch (just to offer some examples) were inferior 
measures when compared to watts per gallon? Now, you're going to ask, 
"who cares?" I do, and we all should. If watts per gallon says I need 
415 watts over my 135 gallon for growing XYZ plants when I really only 
needed 300 watts, that's a big dent in my pocket book and not something 
I call "good enough." Maybe watts per gallon *is* the best rule. My 
whole point is to ask how do we know it's the best without testing other 
methods? And, if we do test other methods, quantitative measurement is 
required. Sure, plus or minus ten percent doesn't matter when 
calculating for the difference between a 29 gallon and a 55 gallon, but 
what if you're calculating the light needed on your brand new 500+ 
gallon tank? A ten percent error in light requirements might cost you 
$150 more dollars in ballast and bulb, and $80 a year in unnecessary 
electricity usage.


-- 
Jerry Baker
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