PAR and PAR Time

Discussion in 'General Reef Discussion' started by whotzler, Jan 4, 2019.

  1. whotzler

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    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
     
  2. KJoFan

    KJoFan I contributed!
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    I think they are not the same. It's about intensity. If the sun were not strong enough to give a plant adequate light to grow/thrive, giving it longer times of the same weak light wouldn't help it grow any better. I think the same applies here.

    Curious what others think though.
     
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  3. OP
    whotzler

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    I am also thinking it would not be the same. Mathematically the same amount of energy would be created, but I think the ability to absorb it at different intensities would come into play, but even this would not explain it completely. I have not heard this talked about before, so just throwing weird questions out there.
     
  4. Adam G

    Adam G Born to Reef!
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    So I have been searching for a study I read about just this topic. I have yet to find it but what I remember is they studied different light intensities on different corals and they could measure the photosynthesis created through the measure of a byproduct chemical produced through the process of photosynthesis.

    At a certain point the coral gets over saturated with PAR and stops producing energy from the light and actually expends energy protecting itself from damage. Getting the coral to this saturation point and holding it there for a period of time is ideal.

    What the study suggested was a reefer should ramp up light to a high level ( like midday sun on the reef) and then ramp it back down. What I took away from it was a peak setting in the middle of the day for a 2 hour period getting the coral to full PAR saturation give or take produced the best growth rates. So say kicking on an extra fixture or ramping up LEDs for 2 hours in the middle of the day would be ideal and then running at say 80% PAR saturation for the rest of the photoperiod.

    For me with a mixed reef I have tried a balance. I have found 350 PAR measured by my Apex PAR meter is the max I care to go at the top of my rockwork where my SPS are located allows acceptable par down lower where my LPS are located with no bleaching or tissue recession. I do not get any bleaching of LPS and my SPS seem to thrive. I ramp up to peak and hold it for 2 hours and then drop down.

    Another thing they found was an 8 hour photo period with 2 hour peak in the middle is just fine. I always thought 12hrs made sense based on the natural reef. I ramp up for an hour in the morning and down for an hour at night and then 8 hours in between for a total of 10 hours with lights on worked for me.

    I will keep digging for the article. I think it was by Dana Riddle but not sure on that. What I just wrote is just the tip of the iceberg of the article.
     
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  5. KJoFan

    KJoFan I contributed!
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    I was going to say, I'm sure Dana Riddle has studied this if not written something on it already.

    But, your comments @Adam G support the theory that just extending the photoperiod at the same intensity would not necessarily translate the same as increasing intensity for at least a given period of time.

    @whotzler I wonder if it just comes down to a difference in units of measurement. While mathematically it should work, time and intensity (PAR) just can't me measured equally.
     
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  6. Nickz

    Nickz Just some guy
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    He gets into it in the first half of this video...

     
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  7. OP
    whotzler

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    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.
     

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