400nm-700nm
[caption id="attachment_204" align="alignleft" width="560" caption="The above spectrograph illustrates the spectral output/PAR output of our PR156_UV fixtures "]
[/caption]What is PAR?
This can be a sticky subject, so let's keep it simple and practical for us reef aquarists! For our uses, PAR is the number of light quanta (particles of light, called photons) that fall in a square meter over the course of one second, that are in between the wavelengths of ~400nm-700nm (nm stands for nanometer, or billionths of a meter).
It as a measurement of the total amount of visible light that shines on a square meter when you start a stopwatch and hit stop afer one second. That's PAR in a nutshell!
Why is PAR important?
PAR is important because it is roughly the measurement of how much usable light energy is available to your corals, anemones, clams - your reef aquarium in general! It's also one of the easiest ways for you to measure the exact amount of light your reef aquarium is getting, which is useful because too little and too much light is bad for photosynthetic invertebrates and plants!
How do you measure PAR?
PAR can be measured with a quantum meter with a detachable, and for aquarium use, a submersible probe.
What are acceptable PAR values?
This greatly depends on the species of coral or other photosynthetic animal, but the acceptable range is roughly 100-450 PAR, measured as PPF (which most PAR meters do). Obviously the low end is preferred by low light corals such as mushroom corals and elegance corals, whereas the high end would be acceptable for shallow water 'SPS' species. For those of you with nature or planted freshwater aquariums, the PAR requirements of plants tend to be lower: between 20-200 PAR, depending on the species.
Read more about PUR
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[...] differs from PAR because the basic definition of PAR is any light in a specific frequency range. PUR is the [...]
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