24 LEDs to cover 16.5"x16.9"?

[Sailfish]

Hi!

 

How do you suggest arranging 24 LEDs to cover a tank with a surface area of 16.5"x16.9"?

 

I'm making a LED fixture for my friend and his D-D tank.

- 24 Cree XR-E 3W LEDs (12 CW &12 RB) with 80 degrees optics

- 16"x8.460" heatsink

 

Help is very much appreciated!

[Sailfish]

Here is some of the patterns I have come up with so far:

 

Option 1 (Based on alternating circles, CW in the middle)

 

Option 2 (Opposite to "Option 1" above)

 

Option 3 (Based on alternating horizontal lines)

 

The tricky thing with arranging these LEDs to cover a almost perfect square is the fact that they are not in the number of 1,4, 9, 16, 25, 36 etc. If they were, the pattern would have the square root of the number of LEDs in each orientation. For example: 16 LEDs=a pattern of 4x4 LEDs.

 

If you picture the classic pattern (LEDs arranged to look like points on a square), the closest to a perfect square you get with 24 LEDs is 4x6 LEDs. On the other hand if you imagine a circular pattern, I would think you could make a pattern more optimal for even coverage, like I have suggested above.

 

One other pattern, if you take a step back and try to acheive the classic "square look", could be:

 

Or maybe, if lighting of the back is less important:

 

Less important to light the front?

 

What do the LED gods think?

 

Edit: I changed out the poor letter patterns with pics from Google Sketchup

[uglybuckling]

I am not one of the LED Gods, but I can tell you what they're going to say....

 

(1) use NW, not CW.

 

(2) At least with Crees, a ratio of 2:1 RB to NW works better than equal numbers, unless you really want your tank to look astoundingly 10k ish.

 

(3) Consider 3ups, and/or the addition of some other color LEDs--in particular read the full-spectrum threads before committing to a RB/CW or RB/NW only array.

 

(4) The number of LEDs you have seems kinda like overkill. Jedi lit his 2x4 foot tank with twelve 3-up stars, meaning twelve NWs and 24 RBs. A dozen of each for something less than 1/3 the area seems like it'd be kind of a lot to me. Of course you can dim it and put it higher above the tank and such, but why buy more LEDs and drivers than you have to?

 

I would suggest (same number of LEDs; full-spectrum build):

 

12 royal blue

6 neutral white

4 true violet ~410nm

1 deep red 660 nm

1 cyan 495 nm

 

[this can also be achieved with six Cree RB-RB-NW 3-up stars, four true violets, and a single OCW 3-up star (see below)]. Then you only have eleven LED stars to figure out positions for on your heatsink.

 

But that's just me. If you really want just a boring blue/white array, you could probably get away with six or eight Cree 3up stars (RB RB NW) over a tank like that. They balance the color to about 14k and make soldering pretty easy. The cost is within a dollar per star of what it would be for individual LEDs, but they're closer together so you get less "disco" effect. Plus fewer connections to solder.

 

There's also this thing called an "Ocean Coral White" 3-up star that has one royal blue (or cool blue, depending on the manufacturer); one deep red 660nm, and one cyan 495nm LED on it. For all practical purposes, it looks pretty much "white" (combining the three primary colors of light--red, blue, and green--gives white) but it still has all those colors in it, so it really makes the reds and greens in corals "pop." They're best run at about 500mA, similar to true violets. This is less than the 3up stars which are best run at 700mA, so you will need a separate LED string with a separate (dimmable) driver on it.

[Sailfish]

Thanks for the detailed post!

 

The thing is that I allready have all of the materials for building this fixture.

That is why I am building it like this.

 

In a future build I will probably add multiple colors, but for now I will make the fixture with what I have.

Also, when I originally bought the parts for this fixture it was ment to go over my tank, not my friend's. That is why I have 24 LEDs. But wouldn't 24 LEDs on a small area just even out the light more than less LEDs would?

[Sailfish]

After doing some more thinking I'm leaning against the "background less important" and the "front less important" patterns (the last 2 patterns pictured in my first post). They are basically the same pattern, only that they are mirrored. This would let my friend choose if he would like to have the two back corners or the two front corners a little dimmer then the rest of the tank, by only rotating the fixture 180 degrees. The "background less important" would be good to dim a corner overflow?

 

What do you guys think?

[Sailfish]

With the patterns above, the spacing between the edge of one star to another will be 0.7 inches. This is because the pattern is supposed to cover a perfect square area.

 

Is this ok, in terms of the rectangular heatsink's ability to remove heat produced by the LEDs?

[Milad LEDGroupBuy.com]

I am not one of the LED Gods, but I can tell you what they're going to say....

 

(1) use NW, not CW.

 

(2) At least with Crees, a ratio of 2:1 RB to NW works better than equal numbers, unless you really want your tank to look astoundingly 10k ish.

 

(3) Consider 3ups, and/or the addition of some other color LEDs--in particular read the full-spectrum threads before committing to a RB/CW or RB/NW only array.

 

(4) The number of LEDs you have seems kinda like overkill. Jedi lit his 2x4 foot tank with twelve 3-up stars, meaning twelve NWs and 24 RBs. A dozen of each for something less than 1/3 the area seems like it'd be kind of a lot to me. Of course you can dim it and put it higher above the tank and such, but why buy more LEDs and drivers than you have to?

 

I would suggest (same number of LEDs; full-spectrum build):

 

12 royal blue

6 neutral white

4 true violet ~410nm

1 deep red 660 nm

1 cyan 495 nm

 

[this can also be achieved with six Cree RB-RB-NW 3-up stars, four true violets, and a single OCW 3-up star (see below)]. Then you only have eleven LED stars to figure out positions for on your heatsink.

 

But that's just me. If you really want just a boring blue/white array, you could probably get away with six or eight Cree 3up stars (RB RB NW) over a tank like that. They balance the color to about 14k and make soldering pretty easy. The cost is within a dollar per star of what it would be for individual LEDs, but they're closer together so you get less "disco" effect. Plus fewer connections to solder.

 

There's also this thing called an "Ocean Coral White" 3-up star that has one royal blue (or cool blue, depending on the manufacturer); one deep red 660nm, and one cyan 495nm LED on it. For all practical purposes, it looks pretty much "white" (combining the three primary colors of light--red, blue, and green--gives white) but it still has all those colors in it, so it really makes the reds and greens in corals "pop." They're best run at about 500mA, similar to true violets. This is less than the 3up stars which are best run at 700mA, so you will need a separate LED string with a separate (dimmable) driver on it.

 

+1 everything he said

 

If you already have the component and are just looking for the layout then you want to cluster the two colors as much as possible to try to recreate what the 3UPs does for you. So side by side, RB and CW and then spread them around the heatsink.

 

Also think ahead on the path of your wires, you will give me a hug for this later.

[MeepNand]

(3) Consider 3ups, and/or the addition of some other color LEDs--in particular read the full-spectrum threads before committing to a RB/CW or RB/NW only array.

 

I would suggest (same number of LEDs; full-spectrum build):

 

12 royal blue

6 neutral white

4 true violet ~410nm

1 deep red 660 nm

1 cyan 495 nm

Totally agree; a good place to get 3-ups is either ledgroupbuy.com if you want crees, or stevesleds.com if you can live with luxeon rebels and want a selection of colors on the 3-ups.

I would also go with the above amount of leds, but with using 1 less violet and 1 turquoise.