Help me understand PAR.

jasert39

jasert39

New member
Our local club has a just received a par meter and the first few members are passing it around and posting their results. Numbers are ranging from 80's to upwards of close to 500 for some bulbs. My question is, how does par equate to coral growth?

Say my bulbs measure a par of 250 (just for easy numbers sake), would the bulbs with the par numbers closer to 500 make corals grow twice as fast? I guess that I am confused because I used to run 250 watt Hamilton 14ks on my tank and my sps grew well and had nice colors, but when I research it's par amount it did not test very highly.

Any anyone out there offer some insight?
 
If you are using Sanjays results then you might be confused. Most of his readings are listed in ppfd not par. There is a distinct difference in readings. Everyone on this board seems to use par when quoting his results or comparing but it is in ppfd. He has several incredible and detailed articles describing how, why, and how it relates to bulbs. I don't remember Hamiltion as being a bad ppfd. on a 400w, magnetic ballast, radium 90,hamilton 96, and xm 104. This is with the 14k and 15k range bulb.
 
I found this article as well when doing my research. Read it. Never found the author. Who wrote it? After reading Sanjays articles I trust his results. I don't know who wrote the other. I did like all of the picture comparisons though. The problem with them though is that I cant see the spectrums. My human eye can't see all of the spectrum or spikes in it. I love numbers and graphs. I guess I'm a nerd or geek when it comes to things like that.lol. Still like to look at pictures though. weird mix. lol
 
As I understand it, PAR is what it is, ppfd is what it is expessed in(quantified). PAR has caught on amounst reefers, probably because its easier to say PAR than ppfd all the time. For our purposes(around here) PAR=ppfd.

Say my bulbs measure a par of 250 (just for easy numbers sake), would the bulbs with the par numbers closer to 500 make corals grow twice as fast? I guess that I am confused because I used to run 250 watt Hamilton 14ks on my tank and my sps grew well and had nice colors, but when I research it's par amount it did not test very highly.
Click to expand...


It doesn't work like that. PAR doesn't = growth. You need a certain amount of PAR for a certain coral to grow. Each is likely different. You also have to have good flow, and parameters, and food helps too, for growth.
IMO once you reach a certain point of PAR(this point is also different for different corals) they top out. They don't need anymore and it does nothing for you...that is my opinion. For my tank I prefer no more than 600 @ 2/3rds from the bottom of the tank. That is the highest I place my SPS anyways, and actually I think 500 is plenty at that level. I want less than 200, prolly closer to 150 on my sandbed. Both those numbers would be under a bulb. With #'s like that you know you'll have a lot of nice varying levels of PAR. That is what I like. Sorry so long, hope this helps somewhat.
 
upon rereading I can see what you mean. I do think it would make more sense to write ppfd. Its only one more letter. I think unit measure or expressed unit measure is important. imho. Thanks for explaining the general thought pattern though.
 
PAR stands for photosynthetically active radiation.
PPFD photosynthetic photon flux density.
Really you should just compare bulbs with these numbers i.e. this one has higher ppfd than this one. This will help you pick the right bulb for your setup.

The higher the par or ppfd, the more usable light is available for the corals to use as energy for photosynthesis. But, photosynthesis can only work so fast, so once saturation is reached you don't need anymore light.
 
A simple parallel would be the amount of sunlight hitting a plant in your flower garden. If you put a flower like a Marigold in full sun, PAR is at its maximum, but all Marigolds in full sun don't grow at the same rate. Other variables like water, temperature, soil type, nutrients, plant genetics, and pests each play a huge factor.
Light is only one of many factors affecting coral growth. It's probably not even the main one.
HTH,
Mariner
 
I think for sps over 400 is decent. I'm not really sure though, maybe somebody else can help out a little more, but from the display readings ive seen posted on here, people are keeping sps well at 400 and over.
 
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