Par readings with ramp up and down

[dumpysauce]

I've got my lights on schedule where they are almost always ramping up or down. its a bell curve type schedule, with very little "plateau".
Therefor its only at peak par for a short amount of time.

My question is this: Say a coral requires 150 par. I measured my par at the peak time to be, say, 200. How do I guess/calculate what the light requirements are for that coral since its going to be in less par most of the day due to the ramping schedule?

Should I check the par at a few points in the day and average them? and use that number for what a coral suggests? Or should I use the peak par as a gage? Since less light is less risk for damage than higher par.

 

[DC Reefer]

You could use the average. I would watch the corals and let their growth and coloration let you know if the lighting is adequate or should be increased/decreased. If the corals are surviving but not really thriving, they may need more light. If you do end up making changes, I find it best to make the changes slowly. If I am ramping up my lights I will usually do it 1 time per week and increase my intensity by 5% or so.

 

[Nano sapiens]

Other than using a data logger, yes you'd need to take multiple measurements over the course of a day's photoperiod. With this info you can determine the DLI (Daily light integral).

Dana's article on the subject:

https://reefs.com/magazine/imitatin...sage-in-a-reef-aquarium-do-we-really-want-to/

I think of peak PAR as more about providing sufficient pigmentation stimulation. Don't need peak for too long, but it has to have enough intensity to get good fluorescence/coloration.

 

[oreo54]

I've got my lights on schedule where they are almost always ramping up or down. its a bell curve type schedule, with very little "plateau".
Therefor its only at peak par for a short amount of time.

My question is this: Say a coral requires 150 par. I measured my par at the peak time to be, say, 200. How do I guess/calculate what the light requirements are for that coral since its going to be in less par most of the day due to the ramping schedule?

Should I check the par at a few points in the day and average them? and use that number for what a coral suggests? Or should I use the peak par as a gage? Since less light is less risk for damage than higher par.

So thinking about this "requires 150 par"

At what 6, 7, 8, 10, 12, 14, hrs per day?
Each would have a different DLI.

 

[ReefRy]

I have a similar schedule and have had similar thoughts. My photo period is 12 hours, from 8a to 8p. At peak, from 1-3, I'm at about 350 par at the tank's highest points and 100ish in the sand. It's been like that for about 10 weeks now and I've had amazing results.

You'll notice pretty quickly if you know your corals if one is getting too much or too little light. I had a fungia that was particularly tricky. After about 6 weeks in this set-up he wasn't looking overly happy, so I correctly surmised he needed more light. A week later and polyp extension was up to about half, and now, close to 100%.

I don't get too caught up with "this coral needs 150 par." I think it's better to try to apply common sense whenever possible. I'm not going to mount a goni in 350 par and I won't try to grow an acro in 50 par, but beyond the obvious I'm not convinced 20 or 30 par either way makes a definitive difference.

I think of it more in terms of what a coral gets each day, same as it would in the ocean. Nothing is constant throughout the day, nor does it need be..just not too much or too little coupled with longterm stability.

 

[dumpysauce]

So thinking about this "requires 150 par"

At what 6, 7, 8, 10, 12, 14, hrs per day?
Each would have a different DLI.

Ya thats what I am wondering. Most people will say a coral need "x" par. But is that peak par? Sustained over a whole day? etc.

 

[Nano sapiens]

Ya thats what I am wondering. Most people will say a coral need "x" par. But is that peak par? Sustained over a whole day? etc.

Here's where this gets interesting! On one end of the spectrum, we have reef aquariums receiving a constant PAR for 10-11 hrs. with maybe an hour of actinic light in the beginning and at the end of the light cycle for a 12-13 hour total light cycle (common setup with non-rampable MH and/or fluorescents)...and something like my little system with LEDs receiving 8 hrs., 2-1/4 hrs' up/down ramping and only 1-1/2 hrs. of all channels at peak intensity PAR.

For the same type of corals, the first example PAR would need to be lower than for the second since the light intensity is nearly constant for a long period of time. A higher peak PAR (up to a point) can be used in the second since it's only at near/full intensity for a relatively short period of time.

Snorkeling in Palau, I saw vast fields of mostly Acropora receiving ~8 hours of near/full intensity sunlight. A short trip the next day to one of the many island groups and I saw mostly mixed corals (lots of LPS/softies, some Acros) that were lucky to get 3 hours of direct mid-day sun (morning and afternoon were really quite dim due to the shadows cast by the hills).

So neither of these extremes is 'wrong' as each type light schema exists in nature and corals are very adaptable (given enough time). And each can be used by the reef aquarist to achieve different effects/goals (more growth vs. more intense coloration, for example). The DLI can also be the same between the two, it's just that the way the light is delivered over the day is quite different. Many people use something between these two extremes and can have great success.

 

[oreo54]

Light Data from a Hawaiian Tidepool

Can we possibly match the amount of natural light in an aquarium?

reefs.com

The tide pool DLI is 22.3, so an aquarium coral receiving 500 µmol·m²·sec in a 12 hour photoperiod is receiving just about as much light as a shallow water (2″ depth) coral does in Hawaii in February. If we bump the light intensity upwards to 525 µmol·m²·sec and the photoperiod remains at 12 hours, we would exceed the natural winter DLI. Of course, we could lower the light intensity and extend the photoperiod and get the same DLI.

Keep in mind it has been found that photosynthesis throttles back at about 350 PAR for high light clades.
At less PAR for others.
Excessive light may help color them (sunscreen effect) but it has a dampening effect in other areas.

There is some conflicting "reports" about this. Kind of odd though but I suppose "growth" can be independent of photosynthesis rates.


Exceding 500 PAR may be excessive regardless.
Anyways from the archives.. Hard to find a live copy..

Feature Article: How Much Light?! Analyses of Selected Shallow Water Invertebrates' Light Requirements

Dana examines the optimal amounts of light required for select stony corals, soft coral and a Tridacna clam, and is intended to complement his previous article 'Too Much Light!' (July 2004).

web.archive.org