36 x 36 tank LED lighting question

[Ruge13]

So I am starting to look at specing out a 36 x 36 x 20+ rimless tank.
Thinking of putting LED lighting over it and need some advice from anyone familiar with LED's.

Not shy about building one myself given that I can't find a stock LED that adequately covers those dimentions.

So, based on what I can find for LED coverage #'s it seems like I need aprox 100 CREE XR-E's. Can anyone confirm? Is this too high? (I hope so!)

If so, the lights + drivers and heat sinks seem like it will be approx $1K project (before I start price hunting). I would be using 70 degree Optics, seems like the better spec for PAR over a wider coverage. Do I have this right?

 

[Ruge13]

So I had that wrong.... 64 LEDS and about $700 I think. Looking at about 10" x 10" sink to place 8x8 LEDS. Gives me room for a couple Red's and a couple moon lights if I separtare the driver for a couple of the blue... I think

 

[kevinpratt823]

If it were me, I would want the overall heat sink to be about 2'x2', leaving about 6" around the edges. This gives you the best coverage/spread. 2" spacing seems like the way to go, and ends up being signifigantly more than 64, with a 2:1 blue/white ratio, dimmable drivers so you can dial in the spectrum. PM me if you'd like to come check out my setups and I'll tell you what I've learned so far. Above all, go big enough for good coverage on the heat sink and you can always add in Led's later.

 

[Ruge13]

Thanks for the offer Kevin, I may take you up on that. I'd love to pick your brain some time. Fortunately time is on my side so I can plan away. The tank won't be set up for a while. I have the budget now, just going to take my time gathering gear.

Did some more reading last night and looking at other builds. Found a couple 20 x 8.5 sinks for short money. So I'm now thinking in the 20 x 17+ range with the larger spread like you said. I originally read 1" spacing but even with optics the smaller 1" spacing for 64-100 LEDs is a smaller point source. So, I'm leaning towards the 2"+ spacing now. Given the tank is not that deep, spread is more my issue than depth penetration which is why I am thinking build vs. off the shelf stock LED fixture. I just can't find the dimentions that work for a cube that size.

As for Drivers, I was thinking the same. # of drivers is confusing me a little. According to Reef LED, I can do 2 strings of 12 on a ELN 60-48 and CREE XRE's. So I am assuming I can get away with 3 drivers, maybe 4 if I go up in # of LEDS.

I was using a 5:3, blue : white ratio to get somethig closer to a 14K. 50/50 is closer to 10K no?

I'm not sure I follow how you get more than 64 LEDS with 2" spacing on a 2x2 sink and 6" around each side. So, I remove the 6" edge, that gives me 12x12 to work with. 2" spacing gives me 48 LEDS? 1" spacing gives me 72. Not sure what I am doing wrong... unless you remove the 6" border. Then the number shoots up.

 

[Ruge13]

Nevermind, I realize what I did. Comes out around 100. those diagrams are wrong. Assumed 2" horizontally bit not vertically. Add that and spreads them out a bit. Out to a 2-3" border and its 10 x 10. Back to my original size but double th spacing. Fits on a 2x2 sink.

 

[Bobbofin]

I have 36 on a 24" x 24" x 24" cube on a 14.5" x 14.5" heatsink, LEDs spreadout 2.25" apart in a 6 x 6 grid square. They are 50/50 blue/white Cree XR-E with 80° optics. It is plenty bright. I actually had to dial them down. You probably make due with 64 in a 8 x 8 grid 2.5" apart and get good coverage. You could make a fixture 23" x 23". Or you could two strips of 36 8-10 wide and 30" long front and back. I'm bringing my fixture to the meeting on November 21 if you want to see it or you could make a roadtrip to NH and I'll spend a couple of hours going over building it. I wouldn't might doing that. Look at this thread>>>> http://www.bostonreefers.org/forums...ED-pendant-14.5-quot-x-14.5-quot-36-Cree-LEDs

 

[kevinpratt823]

Nevermind, I realize what I did. Comes out around 100. those diagrams are wrong. Assumed 2" horizontally bit not vertically. Add that and spreads them out a bit. Out to a 2-3" border and its 10 x 10. Back to my original size but double th spacing. Fits on a 2x2 sink.

What I meant was that you would have 6" from the edge of the heat sink out to the edge of the tank. I would mount the led's 1/2" in from the edge all the way around(no border) and space approx 2". I went with the 5:3 ratio on my 72bow, and if I turn both blues and whites up to 100% it looks more like 10k. It is mostly lps in there, and I am currently running the whites at 35% and blues at 80% for full daylight, this is a nice color close to my radiums. The whites wash out a lot more blue than you may expect, I'm going 2:1 on the setup for the sps tank.

 

[Ruge13]

Thanks for the advice guys, I have seen both of your other threads here. Nice builds. Unfortunately I won't make the meeting this month, I'll be out of the country. I'm sill messing around with the idea. Based on your comments and some other stuff I read with similar comments I think I might get away with smaller than 2x2 and use optics to get and desired spread beyond that. I say that because it seems most are "overbuilt". Not sure if that is true but a lot of people dial them way back. This just tells me they are over powered and can get away with less LEDs at near full power to get a similar result. Does this make sense or am I way off?

If that is the case maybe I can get away with 8x8 on a 17x17 or similr sink.

My concern is overall aesthetics. The 36x36 tank will be rimless. I don't want to cover most of the tank (albeit above the tank) with heat sink. I was originally going with a smaller halide pendant, which is still not off the table. The rockscape will be 2 islands, centered. One for SPS, one for soft corals (zoas, shrooms etc). The emphasis on SPS. Lots of sand real estate. I have had this tank in my head for years now. Anyway, I like tanks that have strong lighting in specific locations. So I like the look of a centered light but faded towards the glass. We'll see.

 

[kevinpratt823]

My only concern with "underbuilding" is having the led's spaced too far apart, making the lighting "spotty" and inconsistent. Even at 2:1 with 2" spacing, the whites end up kind of far apart, but it all still blends. Whatever you decide, good luck, and again, feel free to PM me for a visit.

 

[Ruge13]

Good point.

Also, I hope to have the light at least 12" or more above the tank, which might help this. I do like the idea you brought up about room to expand however. Thanks for the offer, I will be away from this wekend until after thanksgiving. After that, and before I start building anything or ordering parts I would love to talk to you guys. Just thinking out loud for now.

 

[Bobbofin]

I have a 14.5" x 14.5" fixture/heatsink on a 24" x 24" cube. The LEDs are 2.25" apart so they're in a 11.5" x 11.5" 6 x 6 grid on the heatsink and I have plenty of coverage. There are no dark spaces in the tank at all. I think a 8 x 8 grid on a 20" x 20" heatsink would be fine with 70 or 80° optics.