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Old 07/28/2010, 07:22 AM   #1
GPhiAce
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Looking for LED PAR ratings

Does anyone know of a source for good PAR ratings for LEDs? Looking for distribution and depth. I found some from Sanjay http://www.advancedaquarist.com/2010/5/aafeature2 but don't see how that correlates to what others claim that they can compare to 400w MHs. Just interested.

I don't think I am going LEDs on my DT (standard 120), but I may want a project in the future. I am concerned about the penetration and distribution. Would they have a PAR of ~ 300 at 24" depth???? Thanks.


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Old 07/28/2010, 09:08 AM   #2
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well there's alot of variation depending on how the light is built, but on my own personal build i just finished taking about 100 measurements at varying output levels. i haven't figured out a way to post my numbers in a non-confusing way but at the outer edge of the LED's cone of light I took several measurements at 31" and 65% output (light intensity) and got readings between 156 and 242. I'm pretty sure the variation in my numbers is because my sensor placement was not at a consistent width (i.e. left side of the tank the sensor might have been placed at 2" away from the front glass versus 2.5" on the right side).

I couldn't measure directly under center because of my rock placement but based on my middle of tank measurements I would estimate the numbers would be about 75% more than the outer number.

Again, this is just my personal build, i can't speak for the masses. But my OWN personal thoughts (again, just speaking from my own build - don't want to anger the mh gods) are that i have no qualms about keeping sps at any level in my tank.


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Old 07/28/2010, 01:40 PM   #3
GPhiAce
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That helps. What did you use? Driver, optics, etc. Thanks


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Old 07/28/2010, 02:55 PM   #4
blasterman789
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Quote:
I am concerned about the penetration and distribution
The light from an LED is going to be absorbed in salt just as quickly as metal halide. Photons are photons .The only math that's different is with narrow optics LEDs can concentrate more light in a smaller space which is something conventional reef halides can't do. Simple law of squares. With halides coverage is pretty much fixed and your only adjustment is raising or lowering the light a bit. With LEDs depth is no problem with tighter optics, but you need more of them to get coverage.

I'm with g8gxp in that I can easily grow anything I want under LED for about half the energy expenditure of MH. However, I prefer the central light source of MH for aethestic reasons.

Since reef PAR measurements don't guarantee the spectral exclusions between acropora and dope I only trust them for relative testing.


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Old 07/28/2010, 04:54 PM   #5
GPhiAce
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Quote:
Originally Posted by blasterman789 View Post
The light from an LED is going to be absorbed in salt just as quickly as metal halide. Photons are photons .The only math that's different is with narrow optics LEDs can concentrate more light in a smaller space which is something conventional reef halides can't do. Simple law of squares. With halides coverage is pretty much fixed and your only adjustment is raising or lowering the light a bit. With LEDs depth is no problem with tighter optics, but you need more of them to get coverage.

I'm with g8gxp in that I can easily grow anything I want under LED for about half the energy expenditure of MH. However, I prefer the central light source of MH for aethestic reasons.

Since reef PAR measurements don't guarantee the spectral exclusions between acropora and dope I only trust them for relative testing.
Thanks for this. When I said I was concerned about penetration and distribution, I meant overall. I looked a a few sources one LED supplier gave, and the LUX and PAR readings were all above water. The few that they provided thatgave readings underwater were all very low. And as far as distribution, I am questioning the area that each optic will realistically cover. ie, for a 48"x24" area, will 48, 96, 120, x# of LEDs provide 250+ PAR at 24"-30" in saltwater?

I have seen a few different posts, readings, reports of different LEDs and they have all varied. I am just trying to get the best overall understanding of LEDs. I am still reading and learning as much as I can about them. I have not seen any real spectral analysis, however, I do need to read through Sanjay's work again. Thanks for all the information, opinions and experience.


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