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

Jerry Baker wrote:
> True that. The issue, then, is whether lumens are more closely 
> correlated with PAR than watts. Ironically, it is nearly impossible to 
> find lumen ratings on bulbs that appear in Advanced Aquarist bulb PAR 
> studies.

Well, I used the data at Aquabotanic and it seems that lumen ratings are 
much more highly correlated with PAR than wattage. When you perform a 
bivariate linear regression on lumens/PAR you get an r-squared value of 
0.96 with a standard error of 14.76, but when you analyze watts/PAR the 
r-squared is only 0.86 with a standard error of 22.6.

In other words, if you know the lumens of a bulb you can calculate it's 
PAR rating with the following equation*:

PAR = 5.557 + (0.015 * Lumens)

This equation will get you to within about +/- 3.5 PAR units.

However, if you try to calculate PAR from wattage, you would have to use 
the following equation*:

PAR = -9.889 + (1.206 * watts)

This equation only gets you to within +/- 8 PAR units.

*Based upon the bulb data at http://www.aquabotanic.com/lightcompare.htm

Jerry Baker
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