High PAR short time vs. low PAR long time

Bela N

Bela N

New member
Has anyone seen any studies or know if there is any difference between high PAR over a short period of time vs. low PAR for a long period of time, if the total PAR-hrs are the same? For example 200 PAR for 10 hours (2,000 PAR-hrs/day) vs. 400 PAR for 5 hours (also 2,000 PAR-hrs/day). Is one better than the other?

My problem is that I cannot raise our frag tank lights anymore and I think some of the corals, especially new acquisitions, have started to fade in colour (bleaching???). I keep cutting back the time the lights are on, but I am worried I will cut it back too much.

What is the smallest duration the lights can be on assuming high PAR?

Does the photosynthetic "Light Dependent Reaction" max out/shut down at a given PAR level or duration?

Is the ideal number of PAR-hours/day that corals require known? I realize it will vary by species.

Thanks!
 
My LFS owner and friends of mine have their lights on 4 hrs a day everyday except 1 day (7hrs) so I'm not sure if there are studies out there but I know it can be done
 
Bela N said:
Does the photosynthetic "Light Dependent Reaction" max out/shut down at a given PAR level or duration?
Click to expand...

I've read that it peaks at about 4 hours, and there are some people who run 4 on /8 off, resulting in 8 hours of light per 24 hours.

Bela N said:
Is the ideal number of PAR-hours/day that corals require known? I realize it will vary by species.
Click to expand...

I saw a PAR sheet somewhere that had appx. PAR requirements for various species. I would begin with an assumption that their PAR requirements would be that requirement multiplied by around 6, assuming an 8 hour photoperiod with several hours of that lighting being significantly below that peak intensity.
 
Breadman03 said:
I've read that it peaks at about 4 hours, and there are some people who run 4 on /8 off, resulting in 8 hours of light per 24 hours.
Click to expand...

This is interesting. Do you have references or a link? I would love to read more about this.

Just to confirm I understand, anything after 4 hours without a break is a waste of bulb life?

How does intensity play into the equation?
 
PAR (intensity) and photo period are tied together. It's a total sum game. But you max out PAR around 200-400 depending on the coral. Dana Riddle said PAR of 200 was enough for very shallow corals he has been working with. And for shallow corals PAR and PUR are more closely tied together. Deeper corals lose the need for red spectrum and the PAR needs to be higher to get enough blue spectrum which makes up most of the PUR in deeper corals.
 
This is an interesting question I've pondered myself, though I have nothing to add ill bump this so we can get a little more discussion out of it
 
vette.tech said:
This is an interesting question I've pondered myself, though I have nothing to add ill bump this so we can get a little more discussion out of it
Click to expand...

I agree very interesting!

No one has yet addressed the original question:

Is 200 PAR for 10 hours (2,000 PAR-hrs/day) the same to the coral as 400 PAR for 5 hours (also 2,000 PAR-hrs/day)?

or a more extreme example.

Is 150 PAR for 12 hours (1,800 PAR-hrs/day) the same to the coral as 900 PAR for 2 hours (also 1,800 PAR-hrs/day)?

This is the same as asking:

What is the maximum rate of Photosynthesis?
How does PAR effect the rate of Photosynthesis?
At what point will the system ("light Dependent Reaction") max out?

For the science types . . when (time/PAR) will the available stromal space, NADP+ run out and/or what is the maximum storage capacity for NADPH + H+? I am not familiar with coral photosynthesis but assume it uses the same mechanism as other autotrophs. If I am wrong about this please enlighten me.

Thanks
 
There are loads of variable here. But here are some thoughts.

1. it has been shown on several past articles that even in nature some corals shut down when the PAR is excessive. A study I remember reading was don by the University in Hawaii and showed that one particular coral had photosynthesis occur for 4 hours in the morning than shut down for 2 hours around mid day and then continued to photosynthesizes for 5 hours in the afternoon and evening when the PAR decreased.

2. Corals need to run on a cycle that includes photosyntheses periods as well as respiration periods similar to most other plants. In the ideal situation these time period are roughly equal with additional periods where they transition from one state to another.

3. Different corals require different lighting levels. As an example you may have a coral like Seriatopora that needs a PAR of 200 in order to start the photosynthesis process, yet another coral where anything over 200 Par could shut down the photosyntheses process.

4. PAR is really a poor measurement for light when it comes to corals however it is the best we have without ruining spectrum analysis. PAR includes basically all light from 400 to 680 nm. But 95% of corals only need light between 410 and 520 nm. Sure there are chemicals in corals that photosynthesize in the 600 nm range but in nature these same chemicals primely rely on light in the 400 nm range.
 
I can't remember a specific study that addresses the question, however there are studies that may help you. You can also look up the articles cited in "References" that may help.

http://reefkeeping.com/issues/2007-01/atj/index.php
http://www.advancedaquarist.com/2007/3/aafeature1
http://www.advancedaquarist.com/2004/7/aafeature
http://www.advancedaquarist.com/2006/8/aafeature

If you google photoinhibition you will find a lot of studies on the subject, perhaps one also discusses the time factor.
 
If a certain type of coral needs 400w of par 4 hours a day, then it dose not mater if you give it 200w for 8 hours because he will not benefit from it. If you look at it the other way around it will only hurt the coral and maybe bleach/burn it
 
Touring said:
If a certain type of coral needs 400w of par 4 hours a day, then it dose not mater if you give it 200w for 8 hours because he will not benefit from it. If you look at it the other way around it will only hurt the coral and maybe bleach/burn it
Click to expand...

Excellent point!

But, using your example, if that coral can utilize/function between say 400W & 900w, will 2 hours at 800W be functionally the same for the coral as 400W for 4 hours? From a physics point of view, the amount of radiant energy received by the coral will be the same. It looks like the articles referred by sirreal63 & MrIcky may hold the answer.
 
This is where photo inhibition plays a role, as does acclimation and adaptation. There is no coral that I know of that requires a set amount of energy from light, which is just one mood of obtaining food. You will often see the same coral in a wide varie of light conditions with no obvious preference for the amount if light it gets.
 
I remember an article by U of Hawaii as well, I believe it was on pocilopora in tidal pools. The gist of it was that at levels above around 200 PAR photosynthesis is drastically reduced and the energy was dumped as heat by the corals. This is an incredibly low par for a tropical tidal pool, essentially dawn and dusk. Now this doesn't mean that all your coral needs is 200 par, excessive par reduces zoxanthele levels expelling dark pigmented cells and revealing the more colorful ones. So if all I cared about was growth I would use a 150w 10k bulb 12-18" from corals delivering 150-200 par. But for a show tank, probably 250-400w 20k halides depending on tank size. To answer your origional question, simply blasting it with twice the light for half the time is more likely to kill your coral than help it let alone 3x for 1/3. There is a chance than it will be better for the coral than less light, it all depends on the par, spectrum of that par, and the coral. The value needed to begin photosynthesis is very low compared to the restriction value so it's hard to starve your coral of light to the point of death. In biology sum values are borderline irrelivent in many cases, less over a longer period is always better. The energy is the same but if I can spend all day in the sun can you spend an hour on mercury and not get burned?
 
Epicreefer said:
. . . To answer your origional question, simply blasting it with twice the light for half the time is more likely to kill your coral than help it let alone 3x for 1/3. . . . .
Click to expand...

My problem is the reverse, especially with new corals. They are lightening up, almost to the point of bleaching. We are using two 36" Nova Extreme Pros (12 X 36W KZ/Geis T5 Bulbs), welded in parallel, over a 24" wide frag tank. The lights are all the way to the low ceiling (almost a fire hazard). They can not be raised any further. We keep cutting back the time the lights are on. How short a duration can the lights be on? 4 hours? 3 hours? 2 hours? 1 hour? The real solution is simple, purchase a variety of 36" X 24" neutral density filters. Experiment till we find one that cuts the light to the desired level. However this would cost a fortune! We are a high school with 4 tanks (140 gal, 110 gal, 90 gal & 40 gal). I get a total of $700 per year for the tanks, this doesn't even pay for the salt, the rest comes out of my own pocket.

Maybe I should reword the question. If stuck with high intensity (PAR), how short a duration can the lights be on?

Thanks
 
I run 5 hours... When I was acclimating I ran 4 hours for several weeks. At 4 hours I still had growth and good color with my mixed reef (SPS/LPS/zoa). I am led lighting... But regardless, things looked fine at only 4 hours a day. I increased it because I wanted the lights on longer. I don't know if my corals really cared that I have the lights on an additional hour... Another option, if your fixture is 12 bulb... Couldn't you just pull part of the bulbs and decrease intensity that way?
 
Light is not the only cause of pale corals and a lot of the time it has more to do with nutrition than light.
 
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