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How much PAR is enough?

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reedman

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I am curious to see what peoples thoughts are on this. I know most say that the higher the PAR the better, but is there a level where higher levels provide diminished returns?

On the 250W SE bulbs, most seem to produce between 350 and 500 PAR with a few going higher. For a tank depth of 18", I'm wondering if 400 PAR is fine and a 600 PAR really doesn't do that much more for the tanks inhabitants.

I'm not talking about apprearance to our eye, but rather what is used by the animals in the tank.
 

Boomer

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On the 250W SE bulbs, most seem to produce between 350 and 500 PAR with a few going higher

There is no such light bulb that goes that high. You must be lookin' at something wrong ;) The highest PAR bulbs are only around 225 PAR and that is for a 400 W lamp. Some 250's are around 100 + PAR and most 250's are half that. Light over a reef can reach 2,000 PAR. Max photosynthesis for SPS corals can reach between 300 - 600 PAR.


Bulbs

Coral Life 250W, 5,500 K = 64.8 PAR (PPFD)

Iwasaki 250W, 6500 K = 63.7 PAR (PPFD)

Coral 250W, 10,000K = 44.6 PAR (PPFD)

Here is an article on some tested bulbs

http://www.advancedaquarist.com/issues/oct2002/feature.htm
 

reedman

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Hey Boomer.

Here's the link where I got the PAR readings from.
http://www.cnidarianreef.com/lamps.cfm
From the site, I believe he measured with a light meter, but I could be wrong.

I guess my bottom line question is how important is the intensity when looking at a bulb? I'm up for new bulbs soon and was thinking of going to 14K instead of 10K, but it looks like the intesity (PAR) drops off unless you run an HQI ballast overdriving the bulbs.

Thanks!
 

Boomer

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Reed

I don't know how he got his PAR but it is nothing like I've ever seen.

I would get the new XM-10,000 K. That is about the best bulb I've seen as far as testing and actual data.

I guess my bottom line question is how important is the intensity when looking at a bulb?

Depends on what you want to grow and tank dimensions
 

reedman

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Yeah, I trust Sanjay implicitly on the lights. I'm running the XM 10Ks now. My only complaint is that I get a high pitched whine with them that really starts to grate on my nerves and they flicker sometimes. I'm running the Icecap ballasts, so maybe it's not the bulb, but the ballast. Nobody else here seems to have the problem. Maybe I got an early bulb and they have improved them...don't know. I might try them again and see. It's only my sanity on the line...and there isn't much of that left anyway.

Thanks Boomer. Appreciate the comments.
 

Boomer

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Please, Let us not confuse ourselves between PPFD readings and PAR readings... totally different units...


I think you are the one confused :D

The LI-191SA is designed for measuring PAR (photosynthetically active radiation) in applications where the radiation to be measured is spatially non-uniform (such as within plant canopies). To achieve this, the sensor features a sensing area that is one meter in length. The LI-191SA has the quantum (photon) response through the wavelength range of 400-700 nm for PPFD (photosynthetic photon flux density) as generally preferred for PAR measurements, and has an output in units of micromoles per second per square metre where:

1 µmol s-1 m-2 = 1 µE s-1 m-2 = 6.02 x 1017 photons s-1 m-2[/b]

They are one and the same, more

http://www.atmos.umd.edu/~srb/par/02approach.htm

You can also read this by Sanjay

http://www.personal.psu.edu/faculty/s/b/sbj4/aquarium/articles/MetalHalideLamps1.htm


Reed

See my edit up one post
 

Boomer

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Ok, now I see he uses something different, thus needs a conversion to Janjays PAR/PPFD. What ever the case may be PPDF and PAR are exactly the same thing.

Edit

It is different WHEN

It is the PPFD which should be related to dry matter production of plants or CO2 fixation in phytoplankton. Usually, when ***PAR is available in units of W/m**2***, a nominal conversion factor at 485 nm is used to convert it into units of photon flux density. Preferably, such conversion should be done by spectral integration. Since the inference model we use is spectral, it is possible to get an improved estimate of PPFD.

PAR is usually measured in uE and not W/m **2
 
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reedman

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Thanks again Boomer. I read those a while back. I understand (as best I can) the spectrum needs of the corals and those of my (and my wife's) eyes. I just don't quite get the intensity needs.

I have a 75 gallon tank with primarily SPS at all levels of the tank. I am getting pretty good growth out of them and the color is pretty good.

It's interesting to see what everyone thinks THE driving factor for choosing a bulb. There has to be a happy medium between intensity and needs of coral. Otherwise everyone would need 1000W MH to try to meet the intensity needs.

I am under the impression that intensity needs are driven by tank depth and water clarity. The shallower the tank the less wattage/PAR is necessary to provide the light needs of the corals. The deeper the tank (or as water clarity drops) the more intensity you need. Is this a good assessment?
 

Katchupoy

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reedman said:
I am under the impression that intensity needs are driven by tank depth and water clarity. The shallower the tank the less wattage/PAR is necessary to provide the light needs of the corals. The deeper the tank (or as water clarity drops) the more intensity you need. Is this a good assessment?
I agree with you Reedman...

I read a thread that this guy is using only 175 watt bulbs on his 400 gallon tank... Seems not right, but when ask about the dimensions of his tanks... It is 8'x3'x20" (inches in height)

Click Here
 

Stircrazy

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Boomer said:
On the 250W SE bulbs, most seem to produce between 350 and 500 PAR with a few going higher

There is no such light bulb that goes that high. You must be lookin' at something wrong ;) The highest PAR bulbs are only around 225 PAR and that is for a 400 W lamp. Some 250's are around 100 + PAR and most 250's are half that. Light over a reef can reach 2,000 PAR. Max photosynthesis for SPS corals can reach between 300 - 600 PAR.


Bulbs

Coral Life 250W, 5,500 K = 64.8 PAR (PPFD)

Iwasaki 250W, 6500 K = 63.7 PAR (PPFD)

Coral 250W, 10,000K = 44.6 PAR (PPFD)

Here is an article on some tested bulbs

http://www.advancedaquarist.com/issues/oct2002/feature.htm
Boomer, don't forget that PAR varies greatly with distance. Sanjay does his at a specific distance so thats why his levels are lower. the closer you are to the bulb the higher it will be. I have been playing with my PAR sensor for 2 years now and I do all my tests in my tank with 7" of air and 5" of water between the sensor and the bulb and SE AB's on 250 watt HQI ballast will easily be in the 600's. I am running sun Aquatic 10000K SE's now and they are just shy of 600. so you numbers are very dependent on the distance from the bulb you do your measurements.

Steve
 

reedman

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Sounds like there should at least be a similar correlation between bulb studies when it comes to PAR readings. Even if 2 different studies used different distances if one bulb stood out from the pack as having a higher PAR it should in the other study as well.

Back to the original question though. Regardless of what the actual reading is, is there a point of diminishing returns when it comes to PAR levels? How much is enough? Maybe we can take a tank with a depth of 18" and holding SPS & clams. Assume good water clarity per good husbandry for keeping SPS. Do you gain much by having a bulb that is 50% higher than the group average?
 

Boomer

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Reed

I agree with what you and Cesar has said about depth


Steve

Yes, I know that now but never looked at the distances :( I quite familiar with light extinction in water and air. The conversion form the two tables is the Inverse Square Law.

You should see if you can find a use copy of Kirk's book, you would enjoy it greatly;

Light and Photosynthesis in Aquatic Ecosystems

I like you idea of water and air ( I did the same thing with a water proof LUX meter years ago ) but such measurements IMHO should be the same, so everyone is on the same page. It is like people getting lost on the different alk units or SG. Of course the ISL only applies to air, so one would have to get into extinction coefficients for water. That means that yours, for all practical purposes, is more realistic to the hobbyist :D

I don't know if you have seen this or not, so if you haven't see it, I hope you enjoy it ;)


http://www.intl-light.com/handbook/registered.html
 

Boomer

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Then Reed go back to what I said earlier;

Light over a reef can reach 2,000 PAR. Max photosynthesis for SPS corals can reach between 300 - 600 PAR.

Don't forget this is the sun and not a reef bulb. Many will tell you you can't get enough light over a reef tank. I've seen 55 gal tanks with 2 400 W 6,500 K Iwasaki's and SPS doing great. I've never seen a real study on this issue in an actual reef tank....where is there enough light, what is the cut off.........and there are to many variables
 

Stircrazy

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thanks for the link Boomer, I will take a read of that tomorrow as I am just heading to bed, scaned it quickly and looks interesting.

as to the "Light and Photosynthesis in Aquatic Ecosystems" what is Kirk's last name, might make it easier to find.

Steve
 
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