Can you add up PAR values? - The Planted Tank Forum
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post #1 of 6 (permalink) Old 08-17-2016, 04:16 PM Thread Starter
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Can you add up PAR values?

Stupid question about PAR values that I can't seem to find an answer for. Do PAR values simply add up when you have more than one light or is there a complicated formula to figure it out.

What I mean is if you have a light that has a PAR of 30 and add a light with a PAR of 10 will you get PAR 40? Do you just add it up or is there more to it?
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post #2 of 6 (permalink) Old 08-17-2016, 04:48 PM
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Yes and no....
Closer the emitter centers are to each other the more it "adds"...
Think of 2 lights "superimposed" would be like 100% addition across the beam spread. Put one in another room...

"A man with a watch knows what time it is. A man with two watches is never sure."
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post #3 of 6 (permalink) Old 08-17-2016, 05:22 PM Thread Starter
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Okay I think I know what you mean.

So how about this situation....I'm trying to calculate PAR not directly under my lamp but say 18 inches from center....for example, said fixture has PAR of 40 at center but only 20 at 18" off center. If I put a lamp that has a rating of PAR 20 at center 18 inches away from the first fixture would I assume that I would have approximately 40PAR under it? (20 +20)

Just trying to figure out approximate lighting values for the tank I want to set up and want to make sure I understand is correctly.
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post #4 of 6 (permalink) Old 08-17-2016, 05:23 PM
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Quote:
Originally Posted by jeffkrol View Post
Yes and no....
Closer the emitter centers are to each other the more it "adds"...
Think of 2 lights "superimposed" would be like 100% addition across the beam spread. Put one in another room...
Yep, to straight up ADD THEM up one would have to be right over the other one. And of course that does not work.

There are charts that show par values at different depths and angles.
If you can find that chart for your particular light you could get close by adding the values at the various angles and depths.

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Originally Posted by K1963158 View Post
Okay I think I know what you mean.

So how about this situation....I'm trying to calculate PAR not directly under my lamp but say 18 inches from center....for example, said fixture has PAR of 40 at center but only 20 at 18" off center. If I put a lamp that has a rating of PAR 20 at center 18 inches away from the first fixture would I assume that I would have approximately 40PAR under it? (20 +20)

Just trying to figure out approximate lighting values for the tank I want to set up and want to make sure I understand is correctly.
that would get you close enough!!

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post #5 of 6 (permalink) Old 08-17-2016, 05:35 PM Thread Starter
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Okay thanks Guys just wanted to confirm that.

@ichy: Love your profile pic. Reminds me when I was a kid I made a model of the Gill monster. LOL
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post #6 of 6 (permalink) Old 08-18-2016, 02:01 PM
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Okay thanks Guys just wanted to confirm that.

@ichy: Love your profile pic. Reminds me when I was a kid I made a model of the Gill monster. LOL
That avitar is a selfie!! LOL

BUT I think I actually build that model as a kid as well! I think I had the Wolfman too! Ahhh the good ole days when you could sniff glue and not worry about it!
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