Is PAR additive with multiple lighting fixtures?
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Old 07-07-2013, 04:30 AM   #1
zaner123
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Is PAR additive with multiple lighting fixtures?


Thinking about getting a Current Satellite plus for 29g lightly planted tank.

In the future if I want to add more plants, could I add a second current satellite light to increase the PAR?

Basically... if I have two lights with 20 PAR @ 18", is the effective PAR 40?

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Old 07-07-2013, 05:30 AM   #2
Toby_kourtney
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Yep that's how it works :-)
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Old 07-07-2013, 07:10 PM   #3
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It works that way only if the two lights are very close together, or very far from the substrate. It works because both lights are then lighting up at least the center portion of the substrate. If two fluorescent lights are around 6 inches apart, it doesn't work. The extra light added to the light from the first fixture is reduced because of the greater distance to that bulb and the fact that a given light uniformly covers only the area directly under it, with the PAR dropping off farther away, because of the reflector design.
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Old 07-07-2013, 07:25 PM   #4
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Hoppy, that makes sense. I figured that would be the case.

I figure that a Satellite Plus would give me "low-light" at about 18". I just want the option of adding a second in the future to give me closer to "medium-light".

The 29 gallon aquarium is very narrow anyway, so couldn't really space out the lights.
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Old 07-07-2013, 07:33 PM   #5
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Quote:
Originally Posted by Hoppy View Post
It works that way only if the two lights are very close together, or very far from the substrate. It works because both lights are then lighting up at least the center portion of the substrate. If two fluorescent lights are around 6 inches apart, it doesn't work. The extra light added to the light from the first fixture is reduced because of the greater distance to that bulb and the fact that a given light uniformly covers only the area directly under it, with the PAR dropping off farther away, because of the reflector design.
You are assuming that the lights remain in the same plane..
you could always angle them to converge "in the middle"..
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Old 07-07-2013, 10:51 PM   #6
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Quote:
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You are assuming that the lights remain in the same plane..
you could always angle them to converge "in the middle"..
If you use a DIY hood, with the lights mounted inside, this will certainly work, but it would look odd, and be harder to set up if you just placed them on top of the tank. Plus angling the lights could cause a lot of spillover.
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