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

Thomas Barr wrote:
> Folks want to do all sorts of math, that's fine...........but you do not get any good measurement of light that way, nor with Lumens, lux, and what have you.

I believe that almost all of the time aquarists have enough light over 
the tank that these calculations never matter, but I am interested in 
the edge cases. Think of me as the lazy guy at work who wants to see how 
little he has to do before he gets into trouble, but instead of trying 
to dodge work I'm trying to dodge electricity usage.

> Micro moles of photons/m^2/sec is the best unit overall for plant biology.

PAR = umoles/m^2/sec between 400 - 700 nm. In plain English, you're 
counting the number of photons with a wavelength between 400 and 700 nm 
that strike one square meter in one second. One unit of PAR is equal to 
about 602 billion photons striking each square millimeter per second. 
You know that, but just for the record and anyone reading this who might 
not know.

PAR is the best measurement for photosynthetic purposes, but I defy you 
to show me the PAR rating on the label of most of the lights we buy. I 
couldn't even get Hamilton lighting to tell me anything about the bulbs 
they sell other than the CRI. Not even lumens, lux, spectrum, or 
anything else even related to the quality and/or quantity of light. 
Using lumens is flawed, but you have to work with what's available to you.

> These run about 550-2000$, not something hobbyist care to indulge in.

I might spend the money on it just to publish the results here. That 
would be a great deal of entertainment for me, and useful for others as 
well. Nothing better than being able to add to the body of good 
scientific data in the aquarium trade. We need it.

Of course I would probably get an Apogee if I have to fund it with my 
personal cash, but perhaps there is an aquarium club that is interested 
in getting a spherical Li-Cor.

Jerry Baker
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Aquatic-Plants at actwin_com