# Low/Med/High - PAR values



## majorwoo

I know we've kicked this topic around a bunch, and I understand that there isn't set it stone numbers. What I'm confused about, is why two of our stickied threads are wildly different:


http://www.plantedtank.net/forums/10-lighting/160396-led-lighting-compendium.html


> PAR Values(Source) - Thanks Gnomecatcher for the suggestion!
> Values between 10-30 are considered low light.
> Values between 30-80 are considered medium light.
> Values between 80-120 are considered high light.
> Keep in mind that these values are what is currently accepted by the community as accurate, and aren't set in stone.


http://www.plantedtank.net/forums/10-lighting/184368-lighting-aquarium-par-instead-watts.html


> I don't believe there is any consensus about the definition of low, medium and high light. But, here is my definiition, subject to, and almost certain to change:
> Low light - 15-30 micromols of PAR - CO2 is not needed, but is helpful to the plants
> Medium light - 35-50 micromols of PAR - CO2 may be needed to avoid too many nuisance algae problems
> High light - more than 50 micromols of PAR - pressurized CO2 is essential to avoid major algae problems


So I'm not looking to start a fight, just trying to understand if the numbers have just evolved over time and one thread is older, or what?


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## littlefish_

I'm not anywhere near expert level, but I think it makes sense to have the par level for high light at a lower level because high medium light without CO2 can be really problematic. According to Tom Barr, many nature-style tanks have around 50 micromoles of PAR at the substrate, yet they can still grow "high light" plants.


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## Raymond S.

littlefish_ said:


> I'm not anywhere near expert level, but I think it makes sense to have the par level for high light at a lower level because high medium light without CO2 can be really problematic. According to Tom Barr, many nature-style tanks have around 50 micromoles of PAR at the substrate, yet they can still grow "high light" plants.



Yea, what he said...LOL...
Additionally...algae begins under 50 PAR in non injected tanks given they haven't the mass of faster growing plants needed to off set it...
Staghorn algae is said to favor either fluctuating levels of or too low of an amount of CO2 for the light level. Search the Staghorn threads to find the fixture type. Most aren't over about 60PAR guestimated from fixture/tank size.
IMO high light starts lower than 80 PAR...much lower...


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## WaterLife

From what I am hearing, the second "chart"/quote is currently more accurate.


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## majorwoo

The second one (from Hoppy our lighting master) is the one I am used to hearing as well.


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## majorwoo

The plot thickens! Here Hoppy refers to 60 PAR as medium, which exceed the 50 for high in his first post I linked.

http://www.plantedtank.net/forums/20-diy/168999-one-way-design-planted-tank-led-light.html


> A very good PAR to design for is 60 micromols per square meter per second. This is medium intensity light - if you miss the target, you should still have either low-medium light or high medium light, both of which are very usable.


I'm suspecting that somewhere along the way our categories were enhanced/updated. I'll keep poking around


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## PsymonPsays

majorwoo said:


> The plot thickens! Here Hoppy refers to 60 PAR as medium, which exceed the 50 for high in his first post I linked.
> 
> http://www.plantedtank.net/forums/20-diy/168999-one-way-design-planted-tank-led-light.html
> 
> 
> I'm suspecting that somewhere along the way our categories were enhanced/updated. I'll keep poking around


Glad someone else is seeing this too lol. I try to research as much as I can before asking for personal experiences and/or advice. And right now I'm still torn on how to classify and work with the lighting I'm putting on a new tank soon. Hoping this thread gets interesting. :nerd:


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## heel4you

I am going to subscribe to this thread. Very interesting.
I am still planning a high tech 65 gallon (36 x 18 x 25). I have read most all post on lighting on the forum (alot of the info is over my head) and this should clear things up a little bit from muddy to cloudy...LOL


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## Argus

I don't believe the ISO has set the standards for low, medium, and high aquarium lighting.
>

IMO, these categories should not be taken as more than just rough ideas. Different plants have different requirements. Different wavelengths of light have different penetration rates through water. Distance from surface to substrate is not only going to alter overall brightness, but also change the different wavelengths differently. If you have tannins from driftwood in the water, that could change the penetration of certain wavelengths the way a camera filter does. 

Unfortunately, the world is not a simple place. The more precise you try to be the more caveats you encounter. Fortunately, most plants have a range of tolerance to light levels. So, about right is usually good enough.


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## Hoppy

High, medium and low light PAR values are never going to be set in concrete. First, you have to be sure you are talking about the same thing - for me it is the PAR at the substrate level in the middle of the tank, but others may have different definitions. Then you have to define what criteria you use to define the different levels by. Finally, as time goes by we learn more and more and our definitions will change accordingly.

Since the light intensity varies a lot from one spot to another in a typical tank, a single number is always just a crude way to define high, low, etc. light. To be more accurate you would probably have to use a set of numbers or range of numbers. Really about all it is good for now is to decide on whether to use CO2, Excel, or no added carbon.


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## flight50

I have seen that first chart around the web myself. At any rate, I try to target about 50-60 at the substrate with my Hoppy Meter. The substrate should be your base point because this is the furthest light has to penetrate. Balance of nutrients and co2 becomes an important factor when dealing with high par level. The balance usually requires a lot of attention to a tank in the form of tank maintenance. Those show tanks that look awesome, did not just happen overnight. I can guarantee you that without some trial and error, those people didn't have show tank quality displays on their first attempt.


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## majorwoo

Thanks Hoppy, I certainly agree that a range is going to be better then a specific number - after all it's not like plants die at 0-49 PAR, thrive at 50, and die 51+. I also consider my PAR goals to be substrate level midtank when it is full of water. I was simply looking at building a LED setup and when trying to determine the PAR level to aim for (which would certainly vary around the tank) I couldn't decide what my target should be. Us amateurs like myself really appreciate the work people like you have put into our hobby and when trying to research to make the most informed decision we can (analysis paralysis anyone?) we sometimes end up confused what we should be aiming for. 

I already have a pressurized CO2 setup so in my case I was trying to decide what I wanted to grow and how much light I would need to do it. Specifically I looked at LED's and dimming features thinking that might allow me the best of both worlds, so I could aim for high light and back it down some if I wanted to grow plants that couldn't outgrow the algea at a higher light level.

Again, like so many others, I seriously appreciate the work you've put into helping us understand lighting. Can I ask when you are building a "high" light tank do you aim for a certain PAR or do you build the tank and measure the light after and decide what plants go it it based on that?


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## Hoppy

When I build a light I start with how much PAR I want, with the light hanging at some specific distance from the top of the tank. Then I try to overshoot a bit, knowing it is much better to dim the light (LED) or raise it a bit to drop the PAR to what I want. I also spend a lot of time figuring out how to avoid glaring spillover light.

I think that 40-50 PAR is a good design goal, if you don't want high light. And, 60-80 or so is a good goal if you do want high light. With LEDs I used to set up a single LED and get a graph of the PAR vs distance for it, then use that to figure out how many LEDs I would need, and what spacing. With PC bulbs, which I used to use, I already had measurements of PAR vs distance, so I used that to decide how many bulbs and what spacing to use.


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