Re: [APD] light and the w/gal rule

["S. Hieber" <shieber at yahoo_com>]

Tell me again what this increased accuracy is going to
purchase.

sh

--- Jerry Baker <jerry at bakerweb_biz> wrote:

> S. Hieber wrote:
> > Well, if you want to go whole hog, use Pearson's R to
> do a
> > partial regression on all the relevent factors, and
> don't
> > forget to take into account the spectral shift that
> occurs
> > with age and variations that occur coming off the
> > production line, etc. When you're all done, most folks
> will
> > find that they wpg still works well, is close at hand
> and
> > convenient, and works as anything else. It's not like
> there
> > is some critical value of light that has to be obtained
> or
> > else plants won't grow well. 
> 
> There is such a value, but it's probably different for
> individual plant 
> species and aquarium conditions.
> 
> One neat thing about regression analysis is that it
> doesn't matter *why* 
> something is correlated, it just is or isn't. I can
> explain 96% of the 
> PAR output using lumen data alone, and I will be within
> 3.5 PAR of the 
> true PAR value 89% of the time. That's pretty good to me.
> It doesn't 
> really motivate me to go find the source of that other
> 4%.
> 
> Your suggestion gave me an idea. Since lumens are based
> upon almost the 
> same spectrum of light that PAR is, but uses a weighted
> curve of 
> perceived brightness as seen by the human eye, I wondered
> if lumens and 
> watts taken together would make a more accurate predictor
> of PAR than 
> lumens alone. Thank you for the idea. I now have a
> logarithmic equation 
> with an r-squared of 0.98!!! Here's the equation:
> 
> PAR = 0.13 x sqrt(lumens x watts)
> 
> So, for an example let's use an AH Supply 55W bulb. We
> know it's 55 
> watts and has about 4700 lumens. That comes out to a PAR
> of 66. Who 
> knows how true this is?
> 
> -- 
> Jerry Baker
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> Aquatic-Plants at actwin_com
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> 

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