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DIY LED Pendant Light

27K views 164 replies 32 participants last post by  Hoppy 
#1 ·
There are some good reasons for using pendant lights. When a light fixture sits right on top of the tank, the PAR near the top of the tank is always much higher than that near the substrate. So, even if you use a light which gives you very low light at the substrate, up near the top of the tank you have far higher light intensity, making it more difficult to avoid algae problems. When the light is located a foot or more above the top of the tank, the difference in PAR between the substrate and near top of the tank is far less.

Lights hanging high above the tank make in-tank maintenance much easier, and more likely to be done. And, when you are doing it you can easily see what you are doing. Also, pendant lights can look very good.

A major disadvantage of high hanging lights is the spillover light, and the glare. Those can be minimized or even avoided if a well designed pendant light is used.

My low light 65 gallon tank has a LED light sitting right on top, with the PAR at the substrate around 25 PAR, which is definitely low light, but the light shining on the Hamburger Mattenfilter, which extends up above the water surface, is high light, and, I have BBA growing on the filter foam, which has gradually migrated to the whole filter foam surface, making it easy for it to also migrate to the plants.

I want to try using 2 pendant lights, each centered over an 18" square of the 18 x 36 foot print of the tank, with the lights hanging 12 - 18" above the tank. Because I enjoy working with LEDs, I'm building my own lights, based on 10 watt LEDs from Ebay.

To minimize spillover and glare, the LEDs will be mounted inside cylindrical "cans" 4 inches in diameter and 6 inches long. I want the lights to be sturdy, not at all fragile, and I want to add low power red and blue LEDs to improve the color rendition of the cool white 10 watt LEDs.


I found some heatsinks made for 10 watt LEDs on Ebay:


For the "cans" I started out expecting to use 4" aluminum ducts, made for clothes dryer installations. But, then I found some 4" aluminum tube, with .085" wall thickness, on Ebay at a good price, so I chose to use that.

I bought a 12" long piece, and cut it into 4 smaller pieces, using a hacksaw:


I cut two 1/8" long rings, to use as retainers for the heatsink ends, then cut the remaining tube in half, to end up with about 5 7/8" long "cans".

I cut 17/32" pieces out of each of the 1/8" rings to make them fit inside the 4" tubes snugly.


After filing the ends of the rings and tubes to smooth them a bit, I used Loctite to glue the rings inside the ends of the tubes. They are now very tightly attached to the tubes. The heat sinks will fit against the rings, so the heatsink will support the tubes, with the "cans" hanging.

However, the heatsink mounting lugs, 4 places on each of them, are too big to fit into the cans, so I used a hacksaw and file to trim them back to fit into the tubes.


The heatsinks now fit in the tubes, and form the top of each "can".


Each heatsink will have a 10 watt cool white LED mounted in the center, with a blue and a red LED mounted on the sides of the 10 watt one. To expand the mounting surface to accept 3 LEDs, I attached a 1/8" x 1" x 2 1/2" piece of aluminum bar to the heatsink LED mounting surfaces.


The 10 watt LED will be held in place with 2 flathead screws, and the blue and red ones will be cemented in place.

Next will be to get a 10 foot piece of 1/2" electrical conduit, and make 2 hangers from it. To bend the conduit I found a used conduit bender on Ebay for about $12, so I bought it, figuring on relisting it on Ebay when I finish with it.
 
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#4 ·
I purchased the LEDs on Ebay, so they are generic ones, two 10 watt cool white, and 2 each blue and red. They are cheap enough that if they don't perform as I want, I can afford to replace them with better ones.

I also got the LED drivers on Ebay, two 10 watt ones and two 1 to 3-1 watt ones with the latter only costing me $2.53 total. I will run the red and blue LEDs in series. They have different forward voltages so I can't easily run them in parallel. The polished insides of the aluminum "cans" should act to diffuse the red, blue and white colors together enough to avoid colored shadows on the substrate.
 
#7 ·
I'm wishing for low intensity, with the lights about 12-18 inches above the top of the tank. But, I really have no way to guess what I will actually get. If I'm off too far I may try 20 watt LEDs, or 3 Cree LEDs, or who knows what else. My gut feeling is that I will be ok with the configuration I started with.
 
#10 ·
Are you planning on using dimmable drivers or are you just gonna run the leds at full blast and adjust height as necessary?

Also, I see no mention of lenses. Are you running the leds without? Is this to help blend colors, even out PAR, or something else? I have 60 degree lenses on my DIY leds and I kind of hate it. A wider spread would work better for me, but I dont want to lose too much power.

I'm very interested to see how this works for you. The "cans" seem like a great idea to both blend light as well as hide glare. The next led project I build will be a pendant, I think they look very clean and modern and I've been thinking of ideas to hide the glare.
 
#12 ·
For cost savings I gave up on using dimmable drivers, but being able to adjust the intensity by raising or lowering the lights entered into that also.

The basic reason for the cans is to shield the glare, but they also substitute for lenses, in that they confine the light out put to a fairly narrow cone, granted with some stray light from multiply reflected rays. A side effect is the increased blending of the colored LED light with the white light, although that may not be necessary due to keeping the 3 LEDs so close together. And, the last effect is to act as chimneys, to improve air flow past the finned heatsinks. I picked the .085" wall thickness tubing over thin wall sheet aluminum ducts to make assembly design easier and much more rugged, as well as to increase the weight of each pendant so it will be easier to make it hang at a true vertical - otherwise each pendant would be likely to always hang off vertical due to the wire unbalancing it. All of this is just theoretical at this point.

I plan to paint the "cans" today, using flat white spray can paint. My room wall is white, so this should make the lights tend to blend in with the wall. It was a hard choice between white and flat black.

A chronic problem I always have when I DIY something is price creep! I keep having to buy odds and ends at the hardware store or Home Depot, and those little costs really add up eventually.
 
#13 ·
That's a pretty slick idea to use the cans for color mixing, I never would have thought of that. I have a par38 "full spectrum" bulb for reefs, the "disco ball" effect off of it is downright nauseating (maybe I could remove the optics and mount in a can as well). Eager to see how this build turns out!
 
#14 ·
dam this thread is going to make my led pendants on my 300 look derivative. i would love to see the par numbers you get and the color that the pendants produce. my pendants are for a bigger tank and i plan on using 5 of them. im going to use 20 watt bxra at 4k from bridgelux for light and then balance out the color with various 3 watters using a6 inch makers heatsink and a diy reflector that im working on this week. please keep us informed im interested alot in the round reflector with parallel sides. i was planning on a square reflector with a slight outward angle and a 6 to 8 inch depth. thanks again for the post.
 
#18 ·
Now this is weird! (Wired and weird!) I temporarily connected one of my 10 watt LEDs, mounted on its heatsink, to the 10 watt driver for it. Plugged in the power, and it came on. Made an appropriately bright circle of light on the floor, with a well defined boundary, as it should be. So, I lugged everything to my dining area where I set it up to measure PAR and take some photos. Plugged it in and nothing happened. So, I reversed the plug in the wall socket - nothing happened. So, I used an extension cord, with a neon light in the plug telling me the power is there, plugged the LED driver into the extension cord - nothing happened. So, I got my multimeter, and measured the DC voltage at the output of the driver - got a 0 to fluctuating reading. Repeated it a few times - mostly got zero. Unplugged the driver. Just for fun, measured the output voltage for the presumably dead driver - got a few volts, which dropped to zero. What the heck is going on??

I checked the polarity of my connections to the LED several times, and it was correct, for sure. I'm thinking of repeating this with the other driver, but I wish I knew what was going on before I try that.
 
#19 ·
I figured out what the problem was. The LED was not in good enough contact with the heatsink, so it worked only until it overheated and failed. Today I tried the other LED, removing the aluminum bar extension on the heatsink and mounting the LED to the heatsink using 4 screws instead of two. It worked fine this way, with repeated starts and several minutes of trial running.

So, I set it up to measure the PAR vs distance. I used a steel pipe across the backs of two dining chairs, with the electric cable as the support for the light, with everything taped so it couldn't slip or fall. The results are encouraging and disappointing, both.


At a LED to PAR meter distance of 20 inches I got 21PAR, which is too little, but the light is well contained by the "can" so it gives very little spillover outside the main beam. The intensity within that circle of light drops off about 33% from the center to the edge of the circle - also very good. At other distances:



I got 13 PAR at 25 inches, and about 8 PAR at 33 inches, which is about the distance I want to use it at.

I think my next step will be using more efficient LEDs, probably 2 or 3 whites in each can, possibly without the supplemental colored LEDs. I'm still thinking about that step.
 
#21 ·
I found some 20-30 watt LED rated heatsinks on Ebay, which are the same diameter, but heavier, so I just order a couple of those. Now, I need to decide what LEDs to get - probably 20 watt ones. Depending on the dimensions of the heatsinks I may still be able to include the red and blue low wattage LEDs.

There are some 100 watt, 200 watt, and higher LEDs now available. I suppose those are for welding tungsten pieces together??
 
#24 ·
I used thermal paste between the LED and the heatsink extension and between that extension and the heatsink. But, one of the tiny screws holding the LED on went in cross threaded and slightly deformed the edge of the LED so it wasn't in good contact in the middle. From now on I will be using 4 screws if I use that type of LED, which I probably will.

It looks like the 20 watt LEDs might have about the right lumen rating to make this work. I'm still debating that with myself though. I would prefer a 30 watt version, but haven't seen one like that on Ebay.
 
#25 ·
I found several 30 watt LEDs on Ebay and other internet sites. I don't know why I didn't see them before. So, I ordered a couple of them, plus compatible drivers. It now looks like the heatsinks will handle 30 watts only with a fan attached, and it isn't clear from the Ebay listing whether the fan is included or not, although it does say in one place that it is. This project is going to take several weeks, possibly until next year, to be completed. (And, that is if everything goes ok.)
 
#26 ·
If you modify a nice 100mm case fan (it might be a tight fit since your OD is 4" probably) right above the LED's. You probably will have to settle on a 80mm with a pretty hefy width that has a higher CFM rating.

Nice project though, would go wonderful with a smaller cube
 
#29 ·
The reason for using a round aluminum tube for the housing is the great reflectivity of aluminum, even when not polished. The inside is fairly rough, compared to a mirror, but I have been sanding it off and on, getting it smoother and closer to being polished. No, I won't paint it. A square aluminum tube would work also, but would require some attention to how it is hung, so the square beam of light stays aligned with the sides of the tank. The round one is much easier to work with, for that reason.

I did a lot of surfing looking for suitable fans, and found a Titan "TFD9525H12ZP Kukri" http://www.newegg.com/Product/Product.aspx?Item=N82E16835192023 which looks very promising. It has a 90 mm fan, and minimal structure outside so it is largely a round cylinder requiring very little trimming to make it fit the 4" tube. I'm still thinking about how to attach it and be able to easily and neatly hang the assembly. Until I get the heatsinks I won't decide on this.

Haagenize, thanks for the idea!
 
#28 ·
I like the idea of using the can to blend the colors!
Been using a combination of Cold White and Warm White 10W ebay diodes for a while now. Man do they put out a lot of heat! Had to add more cooling fins to my fixture that I originally planned. I don't even want to imagine the output of the 30W.

The waterproof drivers they sometimes come with mostly react nicely to PWM switching, but some do not!
For the people considering these LEDs with the 44mm lenses sold for them on ebay: The resulting cone of light is fairly narrow with a spread of roughly 22 degrees when using the lens + reflector on a 10W diode.
 
#31 ·
If I was starting over I would make the cans about 2 inches longer, but I don't want to spend that much more money on this, so I will make what I have work. There is no guarantee that this will end up working well enough to be useful, but in theory a 30 watt LED will give a bit more light than I need, and the heatsink is rated for up to 30 watts, with a fan, so I like my chances of success.

The red and blue LEDs and their drivers arrived yesterday, but I won't start doing anything with them until I have a working light with just the white LED. If I add the red and blue ones it does block some of the air circulation, which may be critical.

Now, I on the hardest part of a project - waiting for parts to arrive.
 
#32 ·
Watching your build closely - I have a 40 breeder to build lights for and hopefully can piggy-back off your work here. I'm thinking about using the Cree MP-L Easywhite LEDs, which are rated at 20W @ 250mA. How would I simulate a pendant light in your calculator?
 
#33 ·
I have no idea how to simulate a pendant light in that calculator, so I haven't been using it for this. I took PAR readings with a 10 watt LED, then scaled up the claimed lumens for that LED to what should give the PAR I desire, which led me to the 25-30 watt LEDs. If I can get one of the 30 watt ones to work with the design I'm using, I will have data for two of the multiple emitter LEDs, and from that it might be possible to figure out a way to use that for a general calculator for pendant lights.

While I wait for my parts to arrive I have been thinking and reading more. Since it looks like adding the red and blue LEDs to the heatsink will block enough air flow to possibly "derate" the heatsink too much, I am thinking of just adding the red LED to the white one. It looks like the cool white LEDs have plenty of blue light in their spectrum, but may be short of red light only.
 
#36 ·
The tube definitely does help. It semi-collimates the light, giving me a circle of light with a well defined border, almost no light outside that circle, and relatively uniform light in the circle. I had planned to do the measurements without the tube just to verify that, but it was very difficult to do - the heatsink comes back out of the tube only reluctantly. The light "cone" is supposed to be 140 degrees, as I recall, so a lot of the light output of the LED ends up being reflected off the inside of the tube. There is no lens on the LED.
 
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