Spend any time researching or discussing lighting options for your aquarium and the subject of PAR is bound to come up. But what exactly is PAR and why is it important?


aquarium lighting MA Pacific SUN USAPAR stand for photosynthetic active radiation. This is the spectrum of wavelengths whose energy is able to be used by photosynthetic cells in plants, corals, and algae. The wavelengths available for photosynthesis (which is the easiest way to think of PAR) are those between 400-700 nanometers.

  table courtesy of



When PAR is measured it is reported as millimoles of light energy per square meter.  (our astute readers will now point out that a mole is a measure of quantity, and they will be correct as “’light energy” in this case equals “photons”) .  While soft corals and lps can have varied (and relatively low) PAR requirements, sps and clams require at least anywhere from 200- 700 PAR.

aquarium service MA Imagine an Ocean

A sample output graph for a major LED light fixture. The top graph shows the output spectrum, which you would expect given 400-700 nm range of PAR. The bottom graph shows the PAR reading at different depths in the tank.

I hope this helped you understand what people mean when they talk about PAR. Check back next week for a brief explanation on PUR or photosynthetically usable light and it’s bearing on your specific aquarium.





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