PUR vs PAR? What is more important when setting up your LED reef tank lighting? - BRStv Reef FAQs
PAR VS. PUR. At First it was as simple as the number of bulbs we needed then someone measured PAR and told us that was the holy grail and we all need to set our LED’s to a PAR number. Now, we all hear about PUR and that it is a better measurement for aquarium light output.
Here’s the facts
The difference between the two measurements of light is subtle in the name.
PAR is the number one way we measure the intensity of our lights and that is generally accurate for reef aquarium purposes. The thing is it will pick up and measure some wavelengths of light that are not valuable to our application of growing corals. So it is a good but less than perfect tool for measuring and adjusting lights.
This is where PUR comes in which measures the light wavelengths that corals are capable of using and excludes some of the unusable spectrum that a PAR meter will measure.
Why not use a PUR meter?
The answer is clear, because there is no such thing available at a price level for reefers.
PUR is more of a concept or calculation based on a specific organisms’ photosynthetic requirements.
The Seneye Reef Monitor device does have a rough PUR calculation based on a few color sensors but it is still a pretty general idea vs being very precise. It is fair to assume that we will not see a highly accurate coral calibrated PUR meter in our industry within the foreseeable future, it would just be astronomically expensive.
For the most part, the discussion of using PUR vs. PAR only confuses the conversation because it is more marketing hype than it is usable information for the home reefer.
When to consider PUR
There is one area in which the PUR concept is valid and useable to reefers and that is when comparing the output between fixtures.
Classically the method of thought was to simply crank up all color channels to 100% then compare the output measured as PAR. This is misleading because with most LED lights no one would ever run the whites, greens and reds at maximum intensity but these spectrums will show up on the PAR meter.
Some manufacturers decided to use the PUR concept instead to show how they have a more efficient mix of LEDs and the output is maximized for the best usable wavelengths for corals as opposed to maximum PAR.
With modern reef tank LED lights, higher PUR equates to more blue colored diodes and very few whites, greens and reds comparatively. There really is no need to measure this with a PUR meter, a heavier blue or white spectrum can be seen with your eyes.
Another easy way to look at it is if your LED light requires that you dial down the whites by 20% or more, they are using too many white LEDs. This is not necessarily a bad thing; it just means you are paying for LEDs your corals don’t need.
Why you should ignore PUR
Outside of using PUR to compare light fixtures when making your selection, we suggest completely ignoring PUR when setting up your tank and this is why.
A vast majority of the light reefers use these days is blue, which is within the PUR range. While the PUR defenders are right that their mentality is more accurate in terms of usable spectrum, if 80% of the light from your fixture is within the PUR range does it really matter?
Maybe when marketing the light but not in actual function.
Secondly, the entire hobby speaks in PAR numbers because they are measurable and accurate for our needs. That means most people are working with the same inaccuracies and the numbers they share have that factored in. If you try to speak in PUR, the pool for comparison gets a lot smaller and in turn far less useful.
Lastly, we will likely never see a highly accurate PUR meter in our hobby. Trying to explain something you cannot measure is not just a waste of time, it decreases success and increases confusion by adding unnecessary theory that is difficult to act upon.
To learn more about lighting check out this custom Lighting Videos playlist we created that includes a handful of our most valuable aquarium light videos. You will see how various corals respond to light, learn about PAR and why T5 lighting continues to be a very popular choice among advanced reefers.