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Old 05-18-2010, 08:54 PM   #1
Hoppy
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Cheap LED Light?


While browsing Ebay a couple of days ago I found an offer of 5 one watt white LEDs, each with a constant 350mA driver, for around $13 when you add in the shipping. I have been wanting to do some "calibrating" of LEDs to figure out how to design a fixture to light a given size tank to a given PAR. So, I ordered two lots of these, total price about $27. They require a 12 VDC power supply, so I found one on Ebay today for about $9 shipped and ordered that. That will be a 10 LED, 10 watt light for about $36. No Ebay links are allowed here, but you should easily be able to find these if you search awhile.

I don't know how much light I will get from these, which is what I want to determine, so don't expect to light a 55 gallon tank for that price. But, the LEDs are advertised to be 70 lumen minimum output. I think this is promising.

When I get these parts, borrow our club PAR meter and finish testing, I will report what I find out here. Then I expect I will be offering the package on the Swap n Shop forum, since I don't need it. Stay tuned to this channel for further......blah...blah...film at 11:00
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Old 05-27-2010, 08:40 PM   #2
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Yesterday I received the LEDs and drivers - 10 of them. Unfortunately, there are no data sheets of any kind included, so I'm not sure what the 4 connections on the drivers are:


You can see their are two prongs, identical ones as far as I can see, and two wires, one black (really faded to gray) and one red (faded to pink). My guess is the two prongs are the power connections, but I can't see a way to tell the + one from the - one. And I assume the wires go to the LED, but is the red the +? Does anyone know? I hate to connect it and blow it by having reversed connections. The LEDs are star mounted and the solder pads are identified as + and -, so those aren't a problem, just the driver.
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Old 05-27-2010, 09:02 PM   #3
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yeah red is usually +, black -
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Old 05-27-2010, 09:35 PM   #4
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Sounds really neat so far. I have half a dozen unused computer power supplies, ready to put to work.

I agree with red = + and black = - unless they want to screw with you. Do LEDs blow that quickly if you reverse the voltage on them?

Let us know how this turns out, how they compare to your Cree LEDs etc.
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Old 05-31-2010, 04:06 PM   #5
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I have one of the LEDs mounted, connected to its driver, and it works fine, so 8 more to go to fill in my 3 x 3 grid:


This one looks promising, although the light seems more yellow than I expected. I can't tell who manufactured the LEDs or the drivers, or what model they are, but some research should correct that, when I get to it.
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Old 06-10-2010, 10:11 PM   #6
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Well, after 30-40 hours of work, almost all of which was spent trying to figure out how to use the PAR data I got, here is what I have learned:

First, the Ebay 1 watt LEDs, with 350 mA drivers, are definitely good enough to use for a LED fixture for planted tanks, especially tanks less than 16-18 inches high. It takes quite a few of them to do it, but if they are available cheaply, they are easy to work with, and will work fine. The very small individual heat sinks I made don't even get warm, so almost any piece of aluminum will work fine as a heat sink. And, the 350 mA drivers work well at 12 volts, at 10 volts and at 10 volts with current limiting resistors in series.

Second, I now understand a lot better how to determine what configuration of LEDs, both the Ebay ones, and the Cree XR-E 3 watt ones, is needed to give you whatever PAR you want at the substrate level. In fact, knowing the lumen output of any standard LED (no special lens involved) you can figure out how to design a configuration of them to get the PAR you want.

Here is a chart of the PAR output for the Ebay 1 watt LED, both on center and off center:

This lets us figure out the contribution to light intensity of each LED in an array of any spacing. To do this:


Each LED contributes some light to every spot on the substrate. Those that are far from being overhead contribute very little apiece, but there are many of them, so their total contribution is a big part of the total PAR. For example, with an 18 inch square array of LEDs separated by 3 inches, the 4 farthest removed LEDs contribute as much to the total PAR as the LED directly over the spot where the PAR is measured. This is why a single row of 4-5 LEDs down the middle of the tank is not a good way to light an aquarium.

Here is what you can expect if you use the Ebay 1 watt LEDs to make a light:


And, for the Cree XR-E 3 watt LEDs, this is approximately what you can expect from an array of those:


My LED light uses the Cree LEDs, spaced 3 inches apart, but not in a complete array, covering the whole top of the tank. I run them at 425 mA, way below the 700 mA they can easily run at.
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Old 06-10-2010, 10:47 PM   #7
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Very nice write-up and documentation Hoppy. So about $2.50 for a 1W LED incl driver. That's actually pretty nice for LEDs. Not quite T5 range yet.

Pretty set with my lighting at the moment, otherwise it would be awefully tempting.

Did you figure out who the manufacturer of these was? Are they much more yellow than your Cree LEDs? Are they perhaps available in different color temps?
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Old 06-10-2010, 11:09 PM   #8
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The LEDs I have seem to be more like 4000K than 6000K, a bit more yellow than I am used to, but very bright. I just visited Ebay again, and found some Luxeon 1 watt ones for about $0.70 each! You would still need drivers, but the ones I got look like they would cost less than a dollar apiece, and work fine. I tried calculating what would happen if these were used at 1 inch spacing - good light output, but at over 100 per square foot, that's a lot of LEDs! I'm still not at all sure who makes the ones I got.

These are really cheap if purchased not mounted on stars, and their configuration would make soldering them onto stars pretty straight forward. But, only for people at least 20 years younger than me.
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Old 06-10-2010, 11:25 PM   #9
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For me, the sweet spot would be to find current technology 1W LEDs mounted to a star, with driver, with ~6500K, for a buck a piece. Then it would really be comparable to our more common lighting options.

We still wouldn't know much about the lifespan, but if they are slightly under-driven and they don't get too hot it should be good.
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Old 06-13-2010, 04:24 PM   #10
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http://www.plantedtank.net/forums/sw...upply-etc.html if you want to have a cheap LED light.
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Old 06-13-2010, 10:08 PM   #11
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Quote:
Originally Posted by Wasserpest View Post
For me, the sweet spot would be to find current technology 1W LEDs mounted to a star, with driver, with ~6500K, for a buck a piece. Then it would really be comparable to our more common lighting options.

We still wouldn't know much about the lifespan, but if they are slightly under-driven and they don't get too hot it should be good.
Most of the reefers (and CREE manufacturers themselves) claim their 3W XRE's and XPG's last 50,000 hours if driven at their max voltage(I believe). So, theoretically, they should last 10-11 years on your tank. I built an LED light for my reef with CREE's and these things are POWERFUL!

I'm not sure about these 1W eBay LED's though.
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Old 06-13-2010, 11:07 PM   #12
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Originally Posted by chase127 View Post
Most of the reefers (and CREE manufacturers themselves) claim their 3W XRE's and XPG's last 50,000 hours if driven at their max voltage(I believe). So, theoretically, they should last 10-11 years on your tank.
I always wonder how they know that... given that those LEDs are only on the market for a couple of years.

And I take those claims with a grain of salt.
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Old 06-13-2010, 11:27 PM   #13
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Nice

Yeah, I've wondered that too. I made mine thinking that the LED is far better than Halides because there is little to no evap and heat with LED'. And even if it only lasts two years, Thats 2 more bulbs I didn't have to buy and then the cost of LED won out

Plus I got to say I built that awesome thing
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