Please Help with LED Build for 120XH 60X18X26T - The Planted Tank Forum
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post #1 of 3 (permalink) Old 11-12-2013, 09:56 PM Thread Starter
Algae Grower
Join Date: Sep 2013
Location: Melbourne, FL
Posts: 11
Please Help with LED Build for 120XH 60X18X26T

LED Build for 120XH 60X18X26T
I have spent many, many hours researching this on the forum and I am getting information overload. It is time to ask for help as I fear I may be making incorrect assumptions.

Here is what I think so far. Suggestions, improvements, comments, etc would be greatly appreciated.
So here goes:

The tank is 120XH which is 60 long, 18 wide, and 26 tall.

To figure how many rows I need, I used Hoppy"s formula:

2 * H * tan(angle)/4

I used 30 inches for the height since I was going to place the lights 4-6 inches above the tank. Since this is less than 2/3 to 3/4 of the width of the tank, I am planning on two rows.

I am going to use these heat sink pieces which are 5 3/4 X 9 1/8 X 55/64 tall. The bottom 9/32 thick.

At first I was going to make it 9 1/8 wide but it seemed too wide for the tank. I'm thinking of using it as 5 3/4 wide. The fins would be going the wrong way but I think it is heavy enough for passive cooling. Also, spacing the LEDs 3 inches would work out good on the individual pieces. So each half of the tank will have 3 pieces for 27 inches.

I have seen conflicting definitions of light levels.
Values between 10-30 are considered low light.
Values between 30-80 are considered medium light.
Values between 80-120 are considered high light.
Low light - 15-30 micromols of PAR - CO2 is not needed, but is helpful to the plants
Medium light - 35-50 micromols of PAR - CO2 may be needed to avoid too many nuisance algae problems
High light - more than 50 micromols of PAR

Is it a difference in units? I was figuring 100 PAR on Hoppy's spreadsheet. I want medium light with the option to go higher. I could easily go lower by dimming.

Here is what I have come up with:
Height = 30, tank 26, 2 inch substrate, light 6 inches from of tank
Par = 100 ?? too much, too little
Cone angle = 40 since it is over 24" height

I was going to use Cree XP-G since they are $2.50 instead of Cree XM-L at $5.00. All Cool white. Is it worth spending 2X for the XM-L? Do the XM-L produce more light with less heat?

I was going to put 8 blue Cree XP-G in a center row for moonlighting.

Still have not decided on the driver and dimmer questions. It would be great to do the PWM with a Arduino based controller. That Typhon based Arduino with 02Surplus additions looks great. It might be easier with some Meanwell and the simple 0-10V dimming.

With it only being 6 inches above the tank, is the center tank brace going to be a shadow problem?

Is it OK to use a glass canopy over the tank? It has that black hinge material about 1 1/8 inch wide 5 1/2 inches from the front.

Suggestions, corrections?
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post #2 of 3 (permalink) Old 11-12-2013, 11:16 PM
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Location: Sacramento, CA
Posts: 20,304
One suggestion: It seems to be the consensus opinion that we need some blue and red, if not green also, in order to get the color rendition we want. Using all cool white will not give the reddish plants, or the red colored fish the appearance they should have. So, you could add some red and blue LEDs to the mix. But, if they are spaced far from the white LEDs you will get colored shadows on the substrate, so it will work best to cluster the reds and blues with whites. You could use 1 watt red and blue LEDs, and make every other white be a very closely spaced cluster of red, white, blue. They wouldn't add any significant PAR, but they might help the color rendition.

I'm in the process of designing and making some LED pendant lights for my tank now, and I plan to use 10 watt cool white, clustered with a red and a blue 1 watt LED. Until I try it I don't know how effective this will be. But, using 10 watt LEDs might work out well for you too - they seem to produce about 800-1000 lumens of light apiece, per the sellers claims. Just something else to play around with in your head.

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post #3 of 3 (permalink) Old 11-12-2013, 11:34 PM Thread Starter
Algae Grower
Join Date: Sep 2013
Location: Melbourne, FL
Posts: 11
Thanks Hoppy.

I was thinking of putting the a row of blues in the middle. What I probably should do is in the middle row alternate red and blue LEDs every 3 inches without optics. That way there would be a red or blue every 6 inches.

Also, I was thinking of trying to use one of those 4 channel Typhon controllers. Could I hook up 42 LEDs to one channel? Then I could use channels 2 and 3 for blue and red. Leaving channel four open,

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