The Planted Tank Forum - View Single Post - DIY cherry cabinet, LEDs, etc. for 57g rimless (Many pictures)
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post #23 of (permalink) Old 05-16-2011, 07:35 PM
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Join Date: Dec 2005
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Originally Posted by sns26 View Post
I do have 60 degree optics, but haven't decided yet whether to use them. I don't want to raise the light fixture much higher than it is right now. From a design viewpoint (as opposed to a plant happiness viewpoint), 9" above the tank is about right. Most importantly, at this height the wood frame blocks the direct glare from the LEDs unless you bend down and look up. If I were to move it higher, the light would be distracting. And the fixture is already high enough that it doesn't obscure one's view of the entire open top of the tank--that was a major design criterion.
You have obviously done a thorough job thinking out the design tradeoffs you faced. With the 60 degree optics, at 30 inches from the LEDs the light cone would be about 30 inches in diameter, but the cone of maximum intensity would be about 15 inches in diameter, just about perfect for that tank. There would be about 6 inches of the cone that would be reflected back into the tank from the front and back glass, helping to equalize the PAR across the substrate. At the point where the cone intersects the waterline, the diameter would be about 9 inches, which shouldn't be distracting to viewers. Without the optics I think quite a bit of light will spillover the front and back of the tank. The best way to decide, as you have realized, is to try it without the optics to see what it does, than add the optics if they seem to be needed.

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