# PAR testing on a single Cree XP-G



## Dave-H (Jul 29, 2010)

Hello all -

I am designing an LED lighting setup and what I'd really love to do is get PAR data for the Cree XP-G LEDs. Does anyone have one running and a PAR meter, by chance? I've got a PAR meter but I'm still dealing with my canopy build so I haven't gotten the LEDs yet. 

Does anyone know of PAR data for the Cree LEDs??? I would also love to know how the light spreads. I'm planning on suspending the LEDs about 28 inches from the substrate and it would be great to know how far apart they should be to deliver about 40 mms at the substrate. 

thanks, Dave


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## mistergreen (Dec 9, 2006)

Send me your par meter and I'll do some readings for you. I'll get a cree led and everything.


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## redfishsc (Aug 29, 2010)

Yes, I have some data. 

Had a bud with a PAR meter over at my place the other day as we prepared some LEDs for spectral analysis with a radiometer. 

He brought the PAR meter for fun. 

Here is what I got:

My 11g rimless sits under 12 Cree LEDs (6 royal blue XRE, 6 cool white XPG). 
60 degree optics. Suspended at 23" over the substrate. Over a 24" long, 2" wide heatsink.


When driven at about 960mA (my set max current) we got about 100 micromols. I don't recall the exact number but I've done this before and it's pretty consistently between 85 and 100 micromols. 

I don't run them at full current. I run them about 1/3 current, maybe half. But full current will consistently yield me 85-100 micromols at 23". The tank is only 9" deep, so if it were deeper, it may be a touch higher since the water tends to concentrate the beam pattern a little more.


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## pomby27 (Jan 27, 2004)

got any pictures to show?


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## Dave-H (Jul 29, 2010)

redfishsc said:


> Yes, I have some data.
> 
> Had a bud with a PAR meter over at my place the other day as we prepared some LEDs for spectral analysis with a radiometer.
> 
> ...


Very interesting. But hard to imagine how much PAR a single LED would put out. If I knew that and the spread it would be much easier to plan the light setup.

Are there any lenses? How is the spread?


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## redfishsc (Aug 29, 2010)

You guys may find this article quite fascinating. 

http://www.advancedaquarist.com/2010/5/aafeature2


Please note that the PAR numbers that are reported here wouldn't change much if they were all swapped out to "white LEDs only" because, according to the PAR meters, royal blue and white LEDs tend to put out VERY similar PAR numbers at the same drive current. 




pomby27 said:


> got any pictures to show?


Unfortunately not. I've checked the PAR of my array with several meters, just whenever my reefkeeper buds are over for a visit, and it's pretty consistent.

So I didn't really think to take data, sorry. I regret that I didn't. 

My tank is only 9" deep though lol so it would be kinda hard to get much more data than "bottom" numbers .





Dave-H said:


> Very interesting. But hard to imagine how much PAR a single LED would put out. If I knew that and the spread it would be much easier to plan the light setup.
> 
> Are there any lenses? How is the spread?


My array sits about 23-24" from the substrate and uses 60 degree optics. 


I don't have any data about PAR numbers and the light spread, but we will be having some PAR numbers coming up in about 1-2 months for A WHOLE LOT of LEDs and LED combinations--- along with spectral analysis. More news to come at 11.


For what it's worth, we hit over 14,000 micromols on a SINGLE royal blue Cree XRE at 960mA. Of course, that was with the Licor PAR meter sensor sitting almost directly on the LED's 60 degree lens. The Licor has a much higher "top end" than the Apogee meters, but it's also significantly more costly and not necessarily more accurate at sane PAR levels  


Obviously that's only trivial data (kinda neat though  ). 

Also note that the PAR data from a single LED will be of value only to folks like Hoppy who have this supernatural gift of being able to calculate the total sum of PAR values for multiple light sources that overlap. 

Meaning, the PAR of a single LED (with whatever optic) will only be useful if you know how to calculate how the other LEDs around it will increase the PAR values in any given spot.

Or if you're growing a 64-ounce picotope


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## pomby27 (Jan 27, 2004)

just wanted to see how it looks with 50 50 blues and whites, trying to decide how many blues i want in a 12 led array


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## redfishsc (Aug 29, 2010)

If you run them at equal current, it looks a bit odd. 

See this page, I have pics from last august when I first set it up. I adjusted the white balance of the pics on my computer to look as close to "reality" as I could, on my monitor (an HD monitor). 
http://www.carolinafishtalk.com/for...sion/21349-10-gallons-i-cant-afford-reef.html
It's good to have blues, but not too many. 

On a 12 LED array, 2 blues would probably be a safe start if you don't have the blues independently dimmable (ie, they are on the same driver as the whites). 


Also, using neutral and warm white LEDs will help keep the color balance good. I will be using a mixture of cool and neutral whites, along with some blues in the array I'm building for my 45g cube (I despise warm whites but I'm in the minority).


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## Dave-H (Jul 29, 2010)

I'm still not 100% sure whether I should use cool white, warm, lukewarm, blue, royal blue, or whatever kind of LEDs! Is there an article or other resource that can help me to understand this topic?


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## mistergreen (Dec 9, 2006)

Go for white. The par instrument will register blue light but it's missing the red spectrum. Plants need the blue & red spectrum. Just because blue light has the same PAR as white, doesn't mean it'll grow plants.


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## redfishsc (Aug 29, 2010)

I actually doubt quite seriously that any of us would use enough "blue-only" light to have a spectral deficiency. It would just look too strange and be uncomfortable to look at. The "balanced spectrum" issue is easy to overfocus on. Since we're talking about light emitters than can easily hit 300 micromols in a tank, I think we have a tremendous amount of freedom to just pick an LED combination based 99.5% on what looks good in our eyes. The intensity of these emitters, like T5HO, have really kinda put the whole "must have a balanced spectrum" issue in the past. 

If it looks good to our eyes, and is sufficiently intense (according to the PAR meter), it will probably work just fine for plants.

A blue light actually probably could grow plants all by itself but I suspect the growth would be unusually short and bushy--- this is often observed in terrestrial plants in hydroponics outfits that use more blue-spectrum for certain growth periods. I doubt very seriously that anyone would want to look at a planted tank that was lit that blue-- it would be uncomfortable to look at and ugly, for sure.

Many plants won't flower without a lot of red spectrum, according to what I've been reading. Most of us aren't flowering plants anyhow, but a lack of red wouldn't look right.


Either way, Dave, you would do best to use mostly white LEDs, and the colors you pick will depend on whether you like tanks that look more crisp, clear, white..... or more warm and sunny. 


If you like the clear, crisp, white 10,000K look, use cool whites and royal blues, maybe in a 4:1 or 5:1 ratio (4 or 5 whites). No optics on the blues, you need the most spread possible from them.
I can't say for sure what is best since mine are on dimmable drivers and I just tune them down to whatever I think looks best. 


If you want to play it safe, and hit a middle-road (and get good color rendering in general) then use a 1:1 combination of cool white and neutral white. This will be "mostly sunny" to the eye....


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## pomby27 (Jan 27, 2004)

ended up choosing 10 cool whites and 2 royal blues. lets hope this looks good!


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## redfishsc (Aug 29, 2010)

Should be fine. Keep the two royal blues centered over each half of the tank for the best spread, if the tank is 30" or less.


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