PAR and PAR Time

[whotzler]

How does PAR and time relate?

I will start this out simple.

Is 500 PAR for 1 hr = to 100 PAR for 5 hours?

If I wanted to increase total PAR a coral receives by 10% would it be the same to increase time by 10% as it would to increase the PAR number by 10% for the same amount of time?

To me, mathematically these would all be the same.

 

[saltyfilmfolks]

Yes. That’s correct.
So when adjusting, you can go a. It longer or a bit more intensity.

 

[whotzler]

 

[whotzler]

I got some help from my local club TCMAS on this, and found this video pretty interesting. The first couple graphs explain this very well. The rate of photosynthesis is not on a linear scale. For this coral 50 PAR = a photosynthesis rate of 23 and at 100 PAR it is 37 and at 200 its 44. So in this example the PAR level doubles 50/100/200 but the rate of photosynthesis does not follow the same scale 23/37/44. Doubling PAR from 100 to 200 only increases photosynthesis from 37 to 44, that is a small jump for twice the available energy. But doubling PAR from 50 to 100 brings up photosynthesis from 23 to 37, much more bang for you buck here. Bottom line, it is not that simple, double PAR does not equal double photosynthesis. Find the sweet spot and stay in that range.

 

[jda]

As described, there are some other variables. First, you need to be careful not to saturate the coral with light. 1 hour at 3200 is not good and is not equal to 8 hours at 400 PAR (even 500 in your example might be too much for some coral). Second, you have to have a competent amount of light on the low side - 50 PAR for a shallow water acropora is not going to do much even if you run them for 12 hours. Lastly, 20 hours of light is no good so if you cannot get what you want done in 10-12 hours, then you need more output.

While all of the theory and stuff points to just doing math, I would use this for anything outside of 20-25% on the low or high side. The only time that I would use this theory is if you are just slightly under lighting corals and don't want to buy more light. A great use would be if you had some lights that could do 160 PAR on a mixed reef and you wanted 180-200... then adding a few more hours can get you there.