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

```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
> _______________________________________________
> Aquatic-Plants mailing list
> Aquatic-Plants at actwin_com
> http://www.actwin.com/mailman/listinfo/aquatic-plants
>

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