DIY LED Pendant Light
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Old 11-16-2013, 10:59 PM   #1
Hoppy
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DIY LED Pendant Light


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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Old 11-16-2013, 11:08 PM   #2
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Looks promising, which leds are you planning on using?
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Old 11-17-2013, 03:28 PM   #3
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As usual, another very interesting post Hoppy. Can't wait to see the outcome. I have a radion on my 40B and find the corners are a little too dark, I was thinking maybe some pendant lights. Keep up the good work!
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Old 11-17-2013, 03:38 PM   #4
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Looks promising, which leds are you planning on using?
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.
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Old 11-17-2013, 09:10 PM   #5
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Interesting Build!
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Old 11-17-2013, 09:19 PM   #6
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Subbed, looking good Hoppy. How much par do you think this will be putting out? I know you can't predict but what are you shooting for high med or low?
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Old 11-18-2013, 03:17 AM   #7
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Subbed, looking good Hoppy. How much par do you think this will be putting out? I know you can't predict but what are you shooting for high med or low?
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.
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Old 11-18-2013, 03:45 AM   #8
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I'll take your gut feeling over anyone else, you are the parmaster ya know. Please continue with the updates, if you do get low par I may try this build myself.
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Old 11-18-2013, 05:05 AM   #9
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Looking forward to seeing how this looks.
Thank you for posting.
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Old 11-18-2013, 06:24 PM   #10
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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.
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Old 11-19-2013, 01:21 AM   #11
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with the configuration he is showing there won't be room for lenses
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Old 11-19-2013, 03:18 PM   #12
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Quote:
Originally Posted by Edub View Post
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.
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.
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Old 11-19-2013, 03:27 PM   #13
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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!
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Old 11-19-2013, 06:29 PM   #14
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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.
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Old 11-20-2013, 11:47 PM   #15
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My two 10 watt LEDs just arrived. Here is how it fits on the heatsink assembly:
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