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post #6 of (permalink) Old 11-25-2012, 01:42 AM
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Join Date: Dec 2005
Location: Sacramento, CA
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I would use 60 degree optics, because that prevents any serious spillover light - the individual LED beams would be about a foot in diameter at a foot distance, but would cover the substrate very well, with lots of light reflected off the glass to the substrate. Once you hang a LED light that high above the tank you can get good lighting with either a single row of LEDs or a double row, with the rows just a couple of inches or so apart.

Because the 60 degree optics make the beam be 12 inches in diameter at 12 inches distance, you will want the light to be about a foot shorter than the tank length, to avoid lots of spilled light at each end of the tank. This will reduce the light intensity near the ends, too, so if that isn't acceptable you will need to allow for the spillover someway, perhaps using a deep housing for the light that blocks most of that spillover.

I'm not yet convinced that we need to be concerned about CRI for planted tank lights. If you don't consider that, the light can be a lot simpler, and less prone to having colored shadows in the tank.

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