Thinking of going LED

[EMUreef]

Welp the more and more i think about replacing my MH bulbs as its getting to be that time again... i've been thinking about putting the money i would spend on the bulbs into investing into a DIY LED build.

I just wanna figure out first, how many LED's ill need. I've heard between 48-72.

My tank is a 90g 24" tall, and i plan on hanging the LED's about a foot above the water.
I have a mixed reef sps/lps, SPS mainly mid tank/to a lil higher.

What size heat sink?

i've been thinking about going cool white, neutral white, and royal blue mix. 2:1:1 (RB,CW,NW)

I also think i might need lenses.. though i dunno what kinda spacing im going with yet as this is just in the initial pricing planning stage.

[evilc66]

48 isn't even close to enough, but 72 is about right. Set it up in an 18x4 array with 2" spacing between LEDs per row, and 3" between rows. Add 60 degree optics, and you should have a good setup for a mixed reef, even with the array mounted about a foot over the tank.

At this point, I would just use neutral and royals. Don't bother with cool whites. The color rendition benefits of neutral whites makes it worth using by themselves. There has been a lot of discussion on ratios for neutrals and royals, pointing to a 1:2 ratio, but if you use dimmable drivers, I still think a 1:1 ratio is the way to go, just from a color blending standpoint.

[EMUreef]

Thanks for you input evil! i appreciate it!

[RedfordReefer]

I am curious, Why isn't 48 even "close to enough?"

[rosebud161616]

Agreed I would like to know why also. I have a 24 LED panel over a 24" tank and am getting PAR higher than a 400w MH. Granted I did hang it high and am using 40-60* optics. But I would think using two of 24 LED panels over a 48" wide tank would be plenty.

[Tom@HaslettMI]

I'm no expert but I think getting coverage across the entire 48" tank is the main reason.

Rosebud, how long is your tank, and where are you taking the the PAR reading (center of fixture or off to one side)?

Tom

[rosebud161616]

24" long, 24" tall. I'm talking 400 PAR at the center on the sand bed and 200 PAR on the sand bed at the sides.

[cg5071]

Evil, for your 2 inch between measurements do you measure from the center of the LED or the edge of the star? and why 3" between rows?

[Tom@HaslettMI]

24" long, 24" tall. I'm talking 400 PAR at the center on the sand bed and 200 PAR on the sand bed at the sides.

That sounds pretty good. However, if you doubled your tank length and used a second identical 24 LED arrays wouldn't the top-center of the tank be lacking some coverage and likely have lower PAR?

Tom

[RedfordReefer]

Wouldn't there be the same issue with center coverage with MH lamps?

I am just questioning why the term "isn't even close to enough" was used when a single 24 emitter array has more par at 24" than a 400w MH?

[Tom@HaslettMI]

Wouldn't there be the same issue with center coverage with MH lamps

Possibly. Coverage really depends on how high up a fixture is mounted and the angle of the optic or reflector.

Tom

[Tom@HaslettMI]

Check out XSiVE's tank thread HERE (http://www.captivereefs.com/forum/showthread.php?t=9353)... he's using 72 LEDs on two heatsinks on his 120 gallon. He has a 36 LEDs per heatsink, and you can see he has lower PAR in the center of the tank.

Tom

[evilc66]

The reason that I say that 48 LEDs isn't enough ("not even close" might have been a little harsh) to light a standard AGA 90g, is that most people want pretty uniform light coverage, much like you would see with T5 or PCs. With only 48 LEDs, you would either need to group the LEDs into clusters on each side of the center brace, leaving the ends and the center of the tank dark (relatively speaking), or space the LEDs wide and create very bad color separation issues, and poor light uniformity. Either way, the tank may not be lit as well as it could in all areas.

Increasing the number of LEDs will fill in the gaps of either setup. You can still go with a split group like I mentioned before, but with more LEDs, you can cover a larger area, and create less of a "trough" in intensity at the middle of the tank. 72 LEDs would be necessary at that point, as you would remove a few LEDs that would be over the center brace. 64 LEDs would be more practical then, but it would be laid out the same as an 18x4 array, with the middle two columns removed. The closer you can get the LEDs to the center brace, the less light you lose in the middle.

Now, if you use a setup much like rosebud over a tank like this, you could get strong coverage over the sand bed, but higher up in the tank, PAR levels will be less. Not a good situation if you want to put light loving sps up there. It seems to be less of a problem for rosebud with the fixture mounted high over the tank, but if it's mounted lower, the problem becomes greater.

Keep in mind that I'm suggesting this from a coverage standpoint, and not for intensity. I'm also not saying that anyone is wrong in their setup, or that I'm 100% absolutely right, but this is a pretty common setup that works well, and has very uniform light output.

[rosebud161616]

OK that makes sense. I did not want even coverage in my tank. I wanted to be able to have really high PAR for SPS (to the point that I could keep SPS on the sand bed if I really wanted to) and then be able to keep LPS also. The way I have it, I can keep SPS in the center from the sand bed to high up, and around the outside I can keep LPS without much problem. In between the LPS and higher light SPS I keep deepwater SPS. It makes for a nice transition for me.

But yeah if you wanted more even coverage throughout, that makes perfect sense.

[Tom@HaslettMI]

evilc,

Thanks for answering that clear and concisely. I was trying to say precisely that but failing at my attempt.

Tom

[evilc66]

After a few more years of practice, it will come easier ;)

[Mike]

OK that makes sense. I did not want even coverage in my tank. I wanted to be able to have really high PAR for SPS (to the point that I could keep SPS on the sand bed if I really wanted to) and then be able to keep LPS also. The way I have it, I can keep SPS in the center from the sand bed to high up, and around the outside I can keep LPS without much problem. In between the LPS and higher light SPS I keep deepwater SPS. It makes for a nice transition for me.

But yeah if you wanted more even coverage throughout, that makes perfect sense.

I understand what you are getting at. I am going the same way with my new build. Highllighting some areas and letting it transition to "deeper" water in others.