Can someone please simplify PAR for me? - The Planted Tank Forum
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post #1 of 5 (permalink) Old 11-12-2013, 10:45 PM Thread Starter
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Can someone please simplify PAR for me?

Just read what PAR is on Wikipedia, and my brain hurts.

Can someone break this down into simpler terms for me?
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post #2 of 5 (permalink) Old 11-12-2013, 11:05 PM
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It's a measure of the amount of light that plants can use for photosynthesis.

The pieces of the spectrum that plants can not use is not included in a PAR measurement.
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post #3 of 5 (permalink) Old 11-12-2013, 11:08 PM
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There is an excellent article here that is pretty straightforward: There is also information on PPF and PPFD which is much more relevant than PAR.
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post #4 of 5 (permalink) Old 11-12-2013, 11:09 PM
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Can someone please simplify PAR for me?

PAR, Photosynthetically Active Radiation, is the light useable by plants to photosynthesize. It's the wavelength of electromagnetic radiation of visible light from 400-700nm (blue to red light).

Basically, what you're measuring is the amount of useable light at a certain point in your aquarium for the plants to use for photosynthesis.
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post #5 of 5 (permalink) Old 11-12-2013, 11:33 PM
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You can use the measurement of PAR right where the plants you are trying to grow are located. That will be a range of numbers - high near the waterline, lower near the substrate. I think, for us, a better use of a measurement of PAR is to substitute for "watts per gallon" as a measure of how much light we have. That requires measuring the PAR at the substrate, in the middle of the tank, and using that number as a measure of how much light the tank has. That is how I use it.

That number should be around 20-35 if you want a low light tank, around 40-50 or a little higher, for medium light, and around 60-100 for high light.

The units of PAR are micromols of photons per square meter per second, but most of use just say 20 PAR, not 20 micromols of photons per square meter per second.

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