DIY LED Pendant Light - Page 3
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Old 11-25-2013, 05:13 AM   #31
Hoppy
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Originally Posted by McShrimp View Post
Have you considered making the can longer above the heatsink?
The chimney effect can often move a great deal of air.
Efficiency being an important consideration, fans can eat up some real power.
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.
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Old 11-29-2013, 12:30 AM   #32
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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?
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Old 11-29-2013, 04:44 AM   #33
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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?
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.
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Old 11-29-2013, 12:01 PM   #34
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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.
In my experience upgrading store fixtures to LED lights, cool white LEDs always have plenty of blue. It's the reds and greens that are lacking - it becomes pretty apparent when you look at meat or veggies under a cool white LED.
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Old 11-30-2013, 01:15 AM   #35
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So im curious. Depending on the light angle output of those LED's I wonder if the output is better or different than when its not in the aluminum tube. Similar to a light tube for a sealing has a high reflectivity rate, does the aluminum tube help at all?
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Old 11-30-2013, 03:23 AM   #36
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So im curious. Depending on the light angle output of those LED's I wonder if the output is better or different than when its not in the aluminum tube. Similar to a light tube for a sealing has a high reflectivity rate, does the aluminum tube help at all?
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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Old 11-30-2013, 11:39 PM   #37
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do you have the name of the emitters you will be using? and the efficiency. seems odd to go through a build without getting very efficient emitters. also do you have the color temp of the emitters. i am hoping to get at least one of my cannons up and running tomorrow. i will have one 30 watt bxra bridgelux 4k , 2 cree xml 7k, 2 different reds, 2 royal blues, 2 cool blues, and one violet and green. the 3 watters will all be run on different drivers so i can see what they do to the appearance of the light. using just the 4k 30 watt emmiter it gave 34 parr 36 inches below the light using a 60 degree optic. i also need to trim and bend and rivet my reflectors which i will be repurposing the pieces i had cut out of light tube aluminum to make diy MH reflectors. i will be trying for a 10 degree out angle on all 4 sides and making it square. sorry for the hijack but following with great interest.
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Old 12-01-2013, 01:51 AM   #38
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You can get loads of information on LEDs, when you use Cree LEDs, and a lot of information for other name brands, but the really cheap ones on Ebay come with a color temperature and lumen rating, and that's about all. The ones I ordered have these specs:
LED Emitter: 30W
Color: Cool White
Output Lumens: 2500-3500LM
DC Forward Voltage (VF): DC 33-35V
DC Forward Currect (IF): 1050MA
Color Temp: 2850-3050K(Cool White)
Beam Angle: 140 degrees
LifeSpan Time: > 50,000 hours

I suspect the color temperature isn't correct, but I won't know until I see them lit up. The driver, which comes with the LED, has these specs:
Driving power: 30w
Model: 10series 3 in parallel
Input Voltage: 85V~265V
Output Voltage: 33-35V
Current:1050mA
Efficiency > 88%
Power Factor >0.98
Operating Temperature: -20~80
Size (L * W * H): 85mm * 26mm * 21mm

The major spec. that attracted me for this combination of LED and driver is:
$5.72 with free shipping

Theoretically I don't need that high a lumen output, so I am thinking of using a parallel resistor to "waste" some of the 1050 mA current, running the LED at a lower current so the heat from it is much less. I would probably shoot for about 700-800 mAmps. At 800 mAmp, I would need a 140 ohm resistor, able to dissipate about 10 watts, in order to bypass about 250 mAmps of the 1050 mAmps driver output. I could get a 25 watt 300 ohm pot from Ebay for about $10, and that would work as a dimmer by bypassing current. If the LED failed the pot would be subjected to 1050 mAmp, about 100 watts until the LED driver failed - a very short time. (Needs more thought!)
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Last edited by Hoppy; 12-01-2013 at 02:13 AM.. Reason: Add another thought.
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Old 12-01-2013, 04:12 AM   #39
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Sweet project, can't wait to see the final product. I'm a fan of the pendants look over tanks.

I totally hear you on the cost creep while taking the DIY route, it can be troubling. But at least you know what's all going into your project, both in materials and attention to detail.
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Old 12-01-2013, 04:33 AM   #40
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Are you sure of that price? That seems like just the led price to me.

Why not just use a 20w led and driver instead of limiting a 30w to 20 ish watts?
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Old 12-01-2013, 04:53 AM   #41
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I like this projekt. Good job.

Some spontanious thoughts:

* Why not incorporate the thick aluminium tubing in the heatsink solution? Thats a lot of cooling potential just sitting there so close to the led.

* As you have discovered, 10w "cheap led" is way to weak for anything but nano.
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Old 12-01-2013, 08:43 AM   #42
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wow excellent price. if the color is decent and they are correct on the lumen rating i may have to get a set of these for a friends new 210 build.
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Old 12-01-2013, 12:45 PM   #43
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…..so wait, are you using any optics with these LEDs or are you trying to use the can as the optic?
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Old 12-01-2013, 02:41 PM   #44
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PM sent

Could you send to me too Hoppy. thanks

Jefff
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Old 12-01-2013, 04:20 PM   #45
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Are you sure of that price? That seems like just the led price to me.

Why not just use a 20w led and driver instead of limiting a 30w to 20 ish watts?
I sent you a PM with the Ebay item I bought. It is definitely listed as both LED and driver.
Theoretically a 20 watt LED will not provide the PAR I want at the distance I want the light to be. If I do this right I will be able to dim the 30 watt LED a little, and be able to dial it in to the PAR I want. Obviously I need to do some more thinking before using the idea of bypassing some of the current through a potentiometer. There is a way to do this safely, but I haven't thought it through yet.

Quote:
Originally Posted by Matsnork View Post
I like this projekt. Good job.

Some spontanious thoughts:

* Why not incorporate the thick aluminium tubing in the heatsink solution? Thats a lot of cooling potential just sitting there so close to the led.

* As you have discovered, 10w "cheap led" is way to weak for anything but nano.
I originally planned for the aluminum can to be part of the heatsink, but I wasn't able to find a circular heatsink that I could easily modify so it would make good thermal contact with the can. Those that are a big enough diameter require a lathe to machine the OD down to match the ID of the can. And, smaller ones have a too small OD to match any available tubing size. That's when I decided to just rely on the can to act as a chimney to enhance the air flow through the heatsink.
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…..so wait, are you using any optics with these LEDs or are you trying to use the can as the optic?
The can is the optic. It collimates the wide beam of light from the LED into a much narrower beam.
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Originally Posted by Sgtreef View Post
Could you send to me too Hoppy. thanks

Jefff
Now that I am switching to a higher wattage LED/driver my parts list is changed. I will wait until I find out if this will work at all, and until I have made any other changes that are needed, before I send out another list of parts.
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