How long can a coral sustain "too much" PAR?

[eamike261]

This might be a somewhat stupid question... but I'm going to rent a PAR meter soon and I want to do a whole bunch of tests while I've got it but I currently have coral in the tank.

For the sake of the questions let's assume the corals get 200-300 PAR right now.

How quickly would I damage my zoas, LPS, and SPS if I turn the light up to 500-700 PAR? Is a minute okay?

Is there ANY amount of PAR that could bleach/severely damage the corals in a matter of a few seconds? Within reason of course... not talking about 100,000 PAR.

 

[davocean]

Interesting thought and question, my first thought is there are many variables, each coral will react differently, and the overall health of that coral and your tank could be a factor, so results could vary among tanks.

 

[jda]

I grow a few zoas, some bounce and jawbreaker mushrooms and a purple wall hammer all under about 600-750 PAR in my frag tank. Consider that they get about 2200 PAR in less than 1 meter of water in the ocean - all of those coral are collected that shallow. Mine are acclimated to this light and just dropping it on them is not always a great idea.

However, you are going to be OK for a few minutes. Do not worry. I would say that it would take 2-4 hours at 2x PAR all at once for the coral to start to expell some zoox.

 

[Dana Riddle]

Short exposure (minutes) to high light intensity most likely will do no lasting harm but there are some caveats. Previous exposure to light must have been high enough to induce production of protective xanthophylls (a long term process.) As for short term responses, given that it takes about 20 minutes for some protective processes to ramp up, we can suppose that this short exposure time is OK - these xanthophylls slow the rate of photosynthesis by shunting light away from the photosynthetic process. Now, to complicate things some, this ramping time depends upon spectrum (red light produced slow conversion of xanthophylls and thus lower/slower protection.) Also consider the effects of shimmer/flicker/glitter - these light pulses caused by a lensing effect of the water's surface produce intense bands of light and, in some cases, have ben shown to be beneficial photosynthetically speaking.
But the short answer is: Don't sweat it.
As for taking PAR measurements, it is better to turn off all pumps producing ripples in the surface. Otherwise, you'll see measurements going very high and low which can be frustrating when trying to get a good idea of light intensities.

 

[eamike261]

I grow a few zoas, some bounce and jawbreaker mushrooms and a purple wall hammer all under about 600-750 PAR in my frag tank. Consider that they get about 2200 PAR in less than 1 meter of water in the ocean - all of those coral are collected that shallow. Mine are acclimated to this light and just dropping it on them is not always a great idea.

However, you are going to be OK for a few minutes. Do not worry. I would say that it would take 2-4 hours at 2x PAR all at once for the coral to start to expell some zoox.

Short exposure (minutes) to high light intensity most likely will do no lasting harm but there are some caveats. Previous exposure to light must have been high enough to induce production of protective xanthophylls (a long term process.) As for short term responses, given that it takes about 20 minutes for some protective processes to ramp up, we can suppose that this short exposure time is OK - these xanthophylls slow the rate of photosynthesis by shunting light away from the photosynthetic process. Now, to complicate things some, this ramping time depends upon spectrum (red light produced slow conversion of xanthophylls and thus lower/slower protection.) Also consider the effects of shimmer/flicker/glitter - these light pulses caused by a lensing effect of the water's surface produce intense bands of light and, in some cases, have ben shown to be beneficial photosynthetically speaking.
But the short answer is: Don't sweat it.
As for taking PAR measurements, it is better to turn off all pumps producing ripples in the surface. Otherwise, you'll see measurements going very high and low which can be frustrating when trying to get a good idea of light intensities.

Thanks for the info! This makes me feel much better about it.

 

[jda]

Be sure and post which PAR meter you are using if you are not sure if they need a correction factor, or not. Some do - some don't. Nearly all will need one if you use it both in and out of the water.

 

[eamike261]

Be sure and post which PAR meter you are using if you are not sure if they need a correction factor, or not. Some do - some don't. Nearly all will need one if you use it both in and out of the water.

Will do. Is it okay to apply the correction factor after taking the measurements? Or is that something I need to know to take accurate measurements in the first place?

 

[jda]

After is right. Some meters need a 1.06 applied, some more like 1.32 and some need none. It can really matter, so write down what kind of meter it is. If it is an Apogee, then they have all of the correction factors on their website.

 

[Dana Riddle]

Another note on PAR meters - the sensor should be cosine-corrected, meaning its measurements are valid even if the sensor is not exactly level. Li-Cor, Spectrum Technologies, and Apogee sensors are cosine-corrected, others don't advertise this.