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Raising the Kessil


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I've been running a single Kessil A360WE about 6" above the water line for over a year.

I am unhappy with the shadowing from the extreme single point lighting and angle, which causes some of my acros to thrive on one side and wither on the other side.

So I bought the Kessil gooseneck extension. After installing it the light is now 13" above the water (which is now within Kessil's recommendation of 1'-2')

Now comes intensity adjustment.

I have been running at 43% intensity and 53% color. A while back I measured the PAR (which I know is a defective measurement for LED but I am going to rely on a *relative* analysis here).

Measured with the light 5" above water, dead center measurements I read the following PAR at 50% color and 50%, 75%, and 100% intensity:


This shows that PAR drops about 13% per inch in water, regardless of the light intensity. The refractive index of sea water is approximately 1.4 while air is approximately 1 (see: http://scubageek.com/articles/wwwh2o.html),so I estimate PAR would drop about 40% faster in sea water than in air. SOOOO that would mean it should drop about (1/1.4 * .13) or 9% per inch in air. Therefore, if I raised the light 7" and want to maintain the same intensity I'd like to figure out a formula to raise the intensity:


Any comments/feedback on this would be very appreciated ....

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I think it may be like a fixed annual percent depreciation calculation. That is, at each inch it's 91% of what it was at the inch above. I only know how to solve this using a table but I am sure there is a fancier formula. So I *think* this is actually the right way to do the final calculation, basically match the expected surface value at the two heights (I am just gonna use relative percent power as a function of power loss per inch). SO I just plugged in my old intensity and figured out what it 'depreciated' to after 6 inches, and then plugged in new intensities until the value at 13" was about the same.


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