How to determine PAR drop off for height above water level

[pompeyjohn]

Hi all,

There is a nifty radion calculator here: https://www.aquaticlog.com/radion

Unfortunately though that is calculated for 8" above water level, and my lights are 20" above the water level.

Is there a mathematical formular that I can use?

Thanks in advance

 

[pompeyjohn]

This is for a six inch deep zoa frag tank. Frags are about 3 inches below surface. Mounting height needs to be up high, so I am trying to work out the right intensity to get ~200. I have a request in for a PAR meter, but it is going to be a week or two before it arrives.

 

[Breadman03]

The Inverse Square Law is what you're looking for. I don't know how accurate this calculator is, but I imagine it can at least get you into the ballpark. Also note that your linked PAR estimator only includes up to G3 Pro.

Inverse Square Law Calculator for Distance and Intensity

Inverse square law states that, intensity is inversely proportional to the square of the distance from the origin. In this calculator, the distance and intensity can be calculated alternatively with the known value.

www.easycalculation.com

 

[pompeyjohn]

Thank you!

I have a G3, so fingers crossed.

At 8" AWL with the light at 100% the calculator suggests 968 PAR for 3" depth. Using that inverse square calculator the value for 20' high is 154.88. That seems really low, but I guess that is a lot of air for the light to dissipate through.

 

[oreo54]

Hi all,

There is a nifty radion calculator here: https://www.aquaticlog.com/radion

Unfortunately though that is calculated for 8" above water level, and my lights are 20" above the water level.

Is there a mathematical formular that I can use?

Thanks in advance

The inverse sq law doesn' t work well for tanks due to refraction and reflection.
Secondly if the light doesn't get into the tank all is just lost regardless.
Gen 3's had a choice of lenses. Assuming you have the " normal" lens at 80 degrees your spot size is 33.5".
So you can figure out the water surface pattern and if a lot of light is lost.
Easier to just see the light output at 2O" on a large piece of paper with the tank outline drawn in it . Any light outside is wasted inverse sq law or not.

Ideally one wants 1OO% on the water surface.
In your case mire like at the frag level.
So what. 29" plus 3" to frag level?
@ 23" spot size is almost 40".

If you look closely at the radion calculator you'll see it doesn' t adhere to the unverse sq rule
2x the distance 1/4 the power.
At 8+1 (9 inches ) 1271 par
At 8 +10 (18 inches or 2x9) 684
1/2 the par not 1/4.....
At 8 + 28" (36 or 2 x 18) 198 par. Though now 3.4 less 684/198.
Point is the inv sq doesn't work well.

Might as well just reverse the calculator assuming you aren' t spilling a ton of light outside the tank.

Try 485... So globally dim to say 50% all channels on full though.

As good of guess as any..

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