The Planted Tank Forum - View Single Post - Lighting an Aquarium with PAR instead of Watts
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Old 07-22-2012, 12:54 PM   #17
Steve001
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Quote:
Originally Posted by Hoppy View Post
PUR = photosynthetically usable radiation, a concept I haven't yet seen a good reason to dig into. Plants use light from the whole spectrum between about 400 and 700 nanometers wave length. Unlike what many people believe, they also use green light, just not as efficiently as they use blue and red light.

If it was hard to get enough light to grow our plants, we would want to get every advantage we could, and look for bulbs that wouldn't waste any light in the green wave lengths, which, if you think about it, would leave us with very drab looking plants. But, the bigger problem we now have is avoiding too much light, not getting enough light. So, why bother with PUR?
I know your position on PUR measurements, so my suggestion was only half serious. I think your charts are a good general guide because all manufacturers of lights fairly much use the same three phosphors, the caveat, but in varying proportions even though they have access to as many as 20 I believe.


Let me present this argument why I feel PUR is important. A PAR meter measures all PAR wavelengths. It's a generalist's tool. The charts you have created do not plot PAR wavelengths vs. micromol, they show total PAR wavelengths in micromols. As you noted plants use green light and likely other wavelengths less efficiently. But other wavelengths most efficiently. How does one determine from the charts what specific wavelengths of PAR you are actually measuring for any particular light source ?
Knowing PUR vs. Distance could avoid this perhaps.
Quote:
But, the bigger problem we now have is avoiding too much light, not getting enough light. So, why bother with PUR?


Aesthetics (CRI) is another matter for a separate discussion.
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