LED Array for a Pico

[neanderthalman]

Thats a good idea fritz, especially since I should have a stupid amount of light. I'm estimating something around 10000-15000 lux at 8", compared to the paltry 400 lux from my PCs. I also have quite a bit of scrap acrylic around, so I'll give it a shot and measure the difference in intensity.

 

I spent as much of the weekend as I could building my new hood. The construction was pretty straightforward, six identical side peices with beveled edges. The back peice was modified to fit the exhaust fan and leave a gap at the back for the wires for the heater and powerhead to go through. The top was cut slightly larger than the side peices, and after it was all glued 'n screwed, I routed the edge flush with the sides. I rounded the top edge and started filling the holes with a glazing compound that I also happen to have on hand. No wood filler on hand tho, but this stuff will be fine. I'm planning to paint the hood black so I don't particularly care that the filler is red. Here's a few pics.

 

 

 

 

 

 

Actually building the array will be next, and most likely more interesting than an empty hood.

 

Edit - On second thought, I may not get as much light as I estimated as I was overdriving the LEDs in my original array. I'm not doing that with this one, so each LED is just a little dimmer than before.

[mattgreene22]

Keep us posted...looks like a neat project.

[neanderthalman]

Crap.

 

I finished sanding the hood tonight and gave it the first coat of gloss white paint to the inside. I started building the array, and after drawing out my plans on the acrylic, I discovered that I had made an error. I'm going to have to wait about two weeks to finish the array because I'm not going to have enough LEDs. A quick count shows 300 LEDs.....and I only bought 200.

 

The good news on that is that I'm going to have more light. Is it possible to have too much light? Am I going to blast the coralline right off of my rocks when I turn it on? I dunno....but I'm certainly going to have to acclimate the tank to the new lights.

 

In the meantime, I'm going to mount and wire the 200 LEDs that I do have. I definitely have to make arrangements to measure the intensity of some MH lights so I can make a direct comparison.

[blulegend]

I don't think it (LED array) will be able to match the intensity, but it will probably have more total light output.

 

Intensity doesn't add...I think.

[neanderthalman]

I think intensity does add together....and I think my LED array may be similar in intensity to MH, and here's why......(warning, long and technical)

 

A lamps output is measured in lumens, which is an indirect measurement of the number of photons emitted per second at a given average energy.

 

If you have two lamps, then you will have double the number of photons emitted, and therefore, double the measure of lumens.

 

If the color temperature is similar, then the average photon energy will be nearly the same. The visible spectrum is a very narrow band, so the average energy of a photon from a 20000K light will be almost the same as a 6500K light.

 

A lights intensity is measured in lux, which is the number of lumens passing through 1 sq. m of area. The intensity of a lamp will therefore decrease with the square of the distance. ie: moving the lamp twice as far away will reduce the intensity of the light to 1/4.

 

I'm starting to think that the LEDs may match a 175W or 250W MH, as I was at a trade show this afternoon, and one vendor was selling HID lamps. I noticed that his 250W MH lights had an output in the area of 10000 lumens. That light output is in all directions, so the lumens are spread over a very large surface area, reducing the lux measurement.

 

The LEDs, however, emit a focused cone of light, so very little light must be reflected downward. This reduces the surface area that the light covers, increasing the lux measurement in the tank. I measured 5600 lux at 8" with only 50 LEDs. I'm going to have six times as many LEDs. It certainly won't increase the intensity by a factor of six, but it will quite likely be double, or at least break 10000 lux.

 

10000 lux is the equivalent to a 10000 lumen lamp (250W MH) spreading light over 1 sq. m. A MH light, as I said, outputs in all directions...so a sphere with a radius of 20cm has a surface area of....probably somewhere in the range of 1sq. m.

 

Now that I've caught my breath, the only way for me to really find out for certain is to put my luxmeter under some MH fixtures.

 

 

I've put the first coat of black paint on the hood, and it looks damn good. No pictures yet, 'cause it still needs a second coat. About half of the LED array has been drilled with pilot holes, and I've placed my order for the other 100 LEDs. Oh boy...can't wait to get this thing going....

[dga]

Originally posted by neanderthalman

Alright, I slapped together four LEDs in series, and it's no real surprise that I'm gettting about 3V across each, and about 20mA current.  Sounds like the full size array is a go this weekend.  

 

 

I'm also going to fit this exhaust fan in the hood above the LEDs.  

 

Its designed to fit in a PCI/ISA slot in the back of a computer, but it's powered by a drive power connector.  I'm going to straighten the attached metal bracket and use it to mount the fan in place.  The LEDs are such a low profile and the fan is such a low profile that the hood isn't going to be overly tall once it's done.

 

 

Thats exactly the fan i have been looking for. could you tell me where it could be purchased?

[neanderthalman]

I bought it at Princess Auto, and I beleive it is a canadian chain. You're in Michigan, so the closest store would be about an hour and a half across the border....and then there's no guarantee that they'll have any 'cause every store has slightly different stuff.

 

Edit - the store is in London, On.

[mushroom head]

neanderthalman-u think i should have LED or PC lighting for a 1/2 a gallon pico?

[mattgreene22]

Please be sure to post lux measurements when you've got the full array up and running. This would then be some the best comparable data on LEDs I've come across regarding intestity and not style....you'd be getting a progressive measure as the number of LEDs rise..very useful. Sounds like it will kick butt so far!

[neanderthalman]

Thanks matt, I'll be sure to post the lux measurements, but the intensity won't double with twice as many LEDs. It WOULD double if you had twice as many LEDs in the same space. I'm expecting some increase, and I hope that I can get 10000 lux out of it.

 

Hey mushroom, I now think that PCs are crap....at least the ones that I had. I posted these pics before, but it's a great comparison in the color difference from PCs to LEDs

 

PCs

 

LEDs

 

The color difference is incredible, and those pics were taken with identical camera settings. LEDs get my vote....

[mushroom head]

Ok. Im going to get LEDs for the lighting. Here is the thread if u want to cheak it out... http://www.nano-reef.com/forums/showthread...&threadid=60307

[mushroom head]

Im thinking of setting up one of these hexes and another pico. I might want you to build me a hood exactly like yours.

[neanderthalman]

I'd be willing to do it mushroom, if you're willing to wait quite a while. It's taken me two weeks to finish the hood, without getting much work done on the array itself.

 

Here's some shots of the finished hood, and the acrylic that I've drilled for the LEDs.

 

 

 

 

 

Now I get to cut and bend the leads of 300 LEDs...well..200...it'll be at least a week until I get the other 100. I think I'm also going to build a small stand to balance out the hood. It looks pretty damn big on top of the tank, so I'm just going to get some 1x1 pine and cut it like the sides of the hood. It'll be like a ring that fits around the base of the tank, so it won't support the tank at all.

[mushroom head]

How the heak did u make all of those holes? Drilling them one by one?

[neanderthalman]

Yep, drilled each one. Took a few hours, and I wouldn't want to try doing that without a drill press. Each hole was actually drilled twice, first with a pilot hole, then with a 5mm drill bit.

[mushroom head]

How much will u sell me a hood and base for this tank?

[neanderthalman]

Hey dga, check out what I found on thinkgeek. There's on online source for the cooling fan. Mushroomhead, I'll send you a pm after I figure out how long it's taken me to build the damn thing.

[dga]

Originally posted by neanderthalman

Hey dga, check out what I found on thinkgeek. There's on online source for the cooling fan.

 

 

cool, thanks for the heads up.

[mushroom head]

Ok. I cant wait to see the hood and base on the tank and i want to see how bright the LED lighting will be.

[Socalsuperhero]

Like you neanderthalman, I'm in the middle of wiring up a 228 led array myself to retrofit my eclipse 5gal corner. I mounted them in 0.025" sheet aluminum which will mount to the inside of the hood with some nylon bolts and standoffs. Not as many led's, but i've also got a 32watt pc in there. My lights alternate white-blue-white-uv in the array...

 

The led's are as follows:

White LED 20000mcd

Blue LED 6000mcd

UltraViolet UV Black Light LED

 

Also figure I'd share this for anyone else planning on bilding an array of their own...

 

http://led.linear1.org/led.wiz

 

And don't forget to use resistors in the array to limit current to the leds. Led's do not have a constant resistance, and cannot limit current, they are iv happy (the more the supply voltage, the more current they draw.) Anywho, not trying to relight the previous flamewar about led's in this thread, just trying to help.

 

 

 

BTW, your setup is looking really good, can't wait to see it finished.

 

Well in addition to the 32 watt pc retrofit, I decided I still wanted more light. My led's arrived yesterday and I've mounted them in a piece of 0.025" aluminum and finished soldering them up in series groups of six for the 24v powersupply. There's 228 of the little buggers, they alternate white-blue-white-uv in the array...

 

The led's are as follows:

White LED 20000mcd

Blue LED 6000mcd

UltraViolet UV Black Light LED

[doncb]

Socalsuperhero,

 

Thanks for the link for the LED array calculator! Could save some work.

[neanderthalman]

That calculator is pretty cool, but I disagree with the need for resistors, as the LEDs themselves behave as a non-linear resistor. The I-V curve is an exponential function, so they are current happy - at higher voltages, they draw exponentially higher currents, and blow themselves up. That's why, on my original array, the difference between the 12V supply and the 13.5V supply caused so much damage.

 

Here's another thought....what is the resistance of the wires and the solder joints, or the internal resistance of the power supply? If you are going to analyze a circuit down to the point where 1 ohm resistors are important, then you need to take all of that into consideration.

 

My final argument against the need for resistors...the proof is in the pudding. The portions of my array that were undamaged have been running for over a month. They survived a nasty nasty heat wave, and I haven't had any problems with LEDs overheating or burning out - even thought they're overdriven in my original array.

 

I like the look of your array socal, it should improve the color of your tank dramatically. Post before and after pics if possible

[neanderthalman]

Oh, what are you using for a power supply?

[Socalsuperhero]

Ok, so I could see getting away without resistors if you keep your voltage right on. In any case, I'm not taking any chance with my setup, if I have to replace these led's in five years it'll be too soon considering the what a pita it is soldering them all together.

 

I'm using a 24dc 1.7A powersupply, with the led's in series of six with 110ohm .25w resistors in each series.

[neanderthalman]

Keeping the voltage right on is the trick, you're right. That's what happened when I changed power supplies, a small voltage increase damaged part of my first array. I don't know if a small resistor would have saved them, but I doubt it, I was already pushing those leds. My intention with this one is to use an old computer power supply, which outputs very clean and consistent 12V DC.

 

Soldering them can be a pain in the ass if you don't have a lot of experience with it. I work in automation, and I do a hell of a lot of soldering, including some nasty little connectors. Imagine soldering 25 joints all within a 3/4" circle. Stupid stupid design. Personally, I don't have a problem with a lot of soldering, and don't find it to be much of a pita. Good equipment helps too. A 60W iron with a chisel tip will heat the joints real quick, much faster than a pencil tip, and you don't need the pinpoint accuracy of the pencil tip.

 

I would like this array to last as long as possible, and the numbers are pretty crazy. If they're rated for 100,000 hours, which is common, then they should last for about 34 years if you keep your tank lit for 8h a day. I wonder how much it would cost to buy 34 MH bulbs