DIY LED Pendant Light - Page 9 - The Planted Tank Forum
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post #121 of 165 (permalink) Old 01-12-2014, 09:14 PM Thread Starter
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So.. You will end up with the pendent ending ~4 inches above the surface? That's unfortunate!

EDIT: Maybe if you lost the 3w LEDs you could use a second narrower can inside the primary one?
Yes, I would prefer that the can end about 6 inches above the top of the tank, but I can live with 4 inches. At least there will be virtually zero spilled light this way.

I think I will get a 4" aluminum vent pipe for dryers to use for the can. It may be larger in diameter than this one, so I may end up with the can even closer to the water. I picked the 4" diameter to match the heatsink, but I suppose I could use a 3 inch diameter without it looking too weird.

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post #122 of 165 (permalink) Old 01-12-2014, 10:40 PM
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Can't you simply add a lens?

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post #123 of 165 (permalink) Old 01-13-2014, 12:14 AM
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My thoughts too but Hoppy wants to mix colours which wont work with a lens.

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post #124 of 165 (permalink) Old 01-13-2014, 01:16 AM Thread Starter
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A lens tends to give you a very intense light in the middle of a decreasing intensity ring. In other words it doesn't give you anything near uniform lighting. This "can" idea does give a nearly uniform circle of light. And, it also mixes up the colors of any multiple LEDs you use. And, as a bonus, it eliminates virtually all of the glare and spilled light.

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post #125 of 165 (permalink) Old 01-13-2014, 01:38 AM
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How about a 90 deg lens in conjunction with the can?
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post #126 of 165 (permalink) Old 01-13-2014, 03:07 AM Thread Starter
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I don't think a 90 degree lens would do anything useful. Unless the lens angle is around 40 degrees the light gets semi-collimated anyway. The lens might reduce the size of the circle of light a little, by reducing the outer, lower intensity part, that caused by light single reflected in the can.

I have a 10 1/2 inch long piece of 4 inch dryer vent duct now, ready to mount on the heatsink, which looks fairly easy to do. If I make it overlap the heatsink by about 1/2 inch I will have my 10 inch can length. That's tomorrow's job!

The aluminum dryer vent ducts come not yet rolled up completely, so they are easy to cut, with scissors, and very shiny polished aluminum. Kind of flimsy compared to my nice .085" wall aluminum tube, but adequate and not too bad looking. http://www.acehardware.com/product/i...ductId=1276784 except the store sells them individually for about $4.50 each.

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post #127 of 165 (permalink) Old 01-13-2014, 05:13 AM
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A lens tends to give you a very intense light in the middle of a decreasing intensity ring. In other words it doesn't give you anything near uniform lighting. This "can" idea does give a nearly uniform circle of light. And, it also mixes up the colors of any multiple LEDs you use. And, as a bonus, it eliminates virtually all of the glare and spilled light.
Actually, the ebay lenses + base combined with a 'collar' to eliminate glare gives a pretty even light distribution on my 10W LEDs. Maybe because the light source is relatively large?

But I must admit, I was quite intrigued by the idea of using only a can..
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post #128 of 165 (permalink) Old 01-13-2014, 03:49 PM Thread Starter
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Actually, the ebay lenses + base combined with a 'collar' to eliminate glare gives a pretty even light distribution on my 10W LEDs. Maybe because the light source is relatively large?

But I must admit, I was quite intrigued by the idea of using only a can..
I started this idea thinking only about eliminating the glare, then noticed that it should help increase the PAR from a 10 watt LED. Now I am determined to see it through as the only "optic" being used to get the PAR and distribution of PAR that I want. So, I'm intrigued too.

Unfortunately, my low cost LED light is now a high cost light, given all of the changes I have made, and parts I have had to discard. It might still be economical if I don't include the cost of the mistakes.

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post #129 of 165 (permalink) Old 01-13-2014, 04:40 PM
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Unfortunately, my low cost LED light is now a high cost light, given all of the changes I have made, and parts I have had to discard. It might still be economical if I don't include the cost of the mistakes.
These kinds of projects have a tendency to do that.. I have spent more money on my 'cheap' 10W (now 30W combined) light than I care to think of. Fried LEDs, drivers reacting badly to PWM switching, just ONE more length of aluminium, the list goes on. But I guess that is the price of learning. And this is not exactly a cheap hobby to begin with!
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post #130 of 165 (permalink) Old 01-13-2014, 05:10 PM
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have you tested it without the can? Im just curious as to what the par is without the can on it.
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post #131 of 165 (permalink) Old 01-13-2014, 06:23 PM Thread Starter
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have you tested it without the can? Im just curious as to what the par is without the can on it.
No, I haven't tested the 30 watt + two 3 watt warm white LEDs minus the can. I will do so soon.

I just ran into another interesting thing: I tested this with the dryer vent duct can, which is very shiny polished inside. I got 20 PAR at 36 inches, but not very uniform. The PAR varied from about 15 to 20, with two peaks off center where the warm white added the most light. I'm going to use 400 grit paper to dull the finish inside to see if that gets me back to where I was. I think I'm getting too sharp an "image" of the light now, due to the better polish of the aluminum. (The opposite of what I expected!)

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post #132 of 165 (permalink) Old 01-13-2014, 07:00 PM
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How about a diffuser somewhere below the LEDs? Might be able to get a decent result that way without damaging the duct.
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post #133 of 165 (permalink) Old 01-13-2014, 07:29 PM Thread Starter
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This is without any can on the light. That's 12 PAR, not 21. And, it is at 36 inches, where I got about 20 with the can, a 67% increase in PAR with the can.



This is after the inner surface of the can has been lightly sanded with 400 grit paper. The PAR dropped from about 20 to 17, still with two "hot spots" off center, apparently in line with the 2 warm white 3 watt LEDs. You can see two dim yellow circles where the warm white LEDs are giving maximum light. But, the light is much better mixed, and the variation in PAR is much less, now dropping to about 15-16 away from the hot spots. Based on this the can gives a 42% increase in PAR. The very bright small circle of light is a direct reflection from the floor of the end of the can.

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Last edited by Hoppy; 01-13-2014 at 07:55 PM. Reason: Add another pic
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post #134 of 165 (permalink) Old 01-14-2014, 03:25 AM Thread Starter
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I tried to use simple geometry to figure out how the PAR reading should vary with the length of the can, at a fixed distance. I used my last data point, with the lightly sanded can as a starting point. From this I figured that a 12 inch long can should give me a maximum PAR in the lighted circle of 20-25. So, I made a 12 inch long can from the rest of the dryer vent pipe I have, and set it up at 36 inches and measured the PAR again:




You can see that I did get the 20-24 PAR that I should get. Of course now the circle of full PAR light is only about 12 inches in diameter, a bit small for an 18 inch front to back 65 gallon tank, but workable I think.

The chart of PAR vs can length, with the red data points the two can lengths I used, and the red line is what I calculate should be the variation with can length, is:


Now, I need to decide whether it is worth it to finish the project. This seems to be a good lighting arrangement for a 40B tank, only 17 inches high, but very questionable for a 65 gallon tank, 24 inches high.

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post #135 of 165 (permalink) Old 01-14-2014, 05:20 AM Thread Starter
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I don't think I will go any farther with this project. It clearly won't be adequate for a 65 gallon tank, and, in fact would only work for a tank 12 inches front to back and 24 inches long. The circle of light is only about 12 inches in diameter at a PAR of 20-25, which is about as low as I would ever want to use. I think the 30 watt LED is just not going to work for a larger tank.

However, if I wanted to spend a lot more money, like $120, I could substitute an array of Cree XM-L high efficiency, high power LEDs and probably make it work. Here is how they would fit in:


Seven of those LEDs would produce about 5600 lumens, about twice what the 30 watt LED is supposed to produce. And, they would be close enough together to produce reasonably uniform light, using the same 4" diameter cans. I think this is still a pretty good approach, but not with the Ebay 30 watt LEDs.

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