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post #18 of (permalink) Old 12-06-2012, 10:06 PM
Algae Grower
Join Date: Jun 2007
Location: River Falls, WI
Posts: 34
Question on optics angles

Hoppy, thanks a lot for the work. I've been planning a LED build for my 200 gallon, full spectrum, and have pieced together a spreadsheet with spectral output of various LED's and what I'd need to have to get xxx illumination. I get numbers fairly close to yours for numbers of LED's.

I've got a question on the spreadsheet (ver 5), related to the half angle/full angle question stated earlier. The documentation says that if you don't use a lens for the LED's, that

Cone angles for bare LEDs, with no optics installed, XP-G, XM-L, XP-E use 70 degrees, XR-E use 50 degrees
When I look at the spec sheets those look like half of the full width half maximum (FWHM) for the bare LED's (for example, for the Cree XPG the spec sheet the spatial distribution is 50% of maximum at +/- 60 degrees, therefore 120 degree half maximum or FWHM).

So should the angles for the bare emitters be 140 (or 120) and 100? Or am I miscalculating what a "60 degree optic" is by assuming it's +/- 30 degrees at FWHM?

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