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naoki

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I'm not sure if this post belongs in "culture" section, but the light source is an important aspect of our slipper culture for us who rely on artificial light. So I thought that some of you might be interested in this.

I was curious about those Chip-on-board (COB) style LED from China. So I saved up my milk allowance and invested $15 to play with this toy.

Here is everything needed:


From right, AC/DC adapter to drive the cooling fan. Some cell phone charger is probably good enough. I wouldn't use those big, super-old ones which aren't efficient. Reflector is made out of tomato sauce can. I put the foil tape (usually used for ducting) inside to make it silver (instead of gold). 30W diode is attached to an old CPU heatsink after putting thin layer of thermal grease. Then at the left, you can see 30W constant current driver (900mA, forward voltage 30-34V DC). The green bottle is the case for the driver. The "listed" spec of the LED is:

30W Warm White
Forward Voltage (VF): DC 33-35V
Forward current (IF): 1050MA
Output Lumens: 2500-3500LM
beam angle: 140 degree



The construction is super easy. 2 wires of the driver need to be connected to AC plug. Then 2 other wires need to be soldered to + and - of diodes. You should solder before attaching it to the heatsink.

Cost:
I got a 30W emitter + constant current driver from ebay (about $15 including shipping). Additionally, you need a AC/DC converter, an old CPU heatsink+fan, and cables with AC plug. But it's likely that you can find these for free or very cheaply. I used a tomato sauce can (+ foil tape) for a reflector. So the total cost for me is $15. It is almost as cheap as 23W CFL + 8.5" clip lamp.

Comparison against CFL:



Both CFL (left) and LED (right) are at the same hight from the floor (about 10"). The photo gives you an idea of the beam spread. Note that for this photo, I didn't have the reflector attached to LED. Reflector makes the lighted area slightly smaller.

Also, both CFL and LED are "warm" white, and they give relatively similar perceived "color". But most florescent lights have only a few (3-5) sharp peaks in the emission spectrum and white LED has a more continuous spectrum.

CFL is Lite Source LT-23SP, 23W 2700K with cheap 8.5" Clamp Light (Commercial Electric 277-894 from Home Depot). Actual measured energy consumption is 23W.

30W LED consumes 30.8W. The cooling fan driven at 6V consumes 2.6W (6W @ 12V, 1.8W @3V, and 3V is probably good enough, though). So total of 33.4W.

Measurement (with Gossen Ultra Pro light meter, 12" from the tip of the light source):

CFL: 300 fc
LED: 550 fc (520 fc without tin can reflector)

CFL: 300fc/23W = 13fc/W
LED: 550/33.4W = 15.6fc/W

So LED provides about 20% more light per watt.

Light spread
To roughly understand the beam spread pattern, I measured right below the light, 6" off-center and 12" off-center. Light is 12" above the measuring plain.

CFL: 100% @ center, 53.3% @ 6" off-center, 23.0% @ 12" off-center
LED: 100% @ center, 65.5% @ 6" off-center, 32.7% @ 12" off-center

So LED has a wider usable spread in this case. In other words, actual advantage of LED is greater than 20%.

misc:
This cheap LED is probably crappy (in efficiency) compared to better COB LEDs such as Bridelux Vero or Cree XLamp CXA. I would say that the output of this cheap ebay LED is better than I expected, and it is super cheap and usable for orchids. We'll see how long it will last. In a long term, you'll probably save money with Vero or CXA than the less efficient, cheap LED even though the initial cost is higher. However, the white LED technology seems to keep changing rapidly, so low initial cost could be a good thing.

If you are not into DIY, you can find preassembled LED flood light (e.g. $30 for 30W), which uses a similar LED. You may need to attach AC plug, but you don't need to solder, and you get water-proofed case and reflector. It seems like a pretty good deal compared to T5HO. But I'm not sure how effectively the heat is dissipated, and how long they will last.

Here is a link to something similar (the link will die eventually):
30W LED Warm Cool White High Power 3300LM Lamp Chip 30W Power Driver 85 265V | eBay
100W LED Warm Cool White High Power Lamp Chip 100W Power Driver AC 85 265V | eBay

LED Flood light example:
10W 20W 50W 100W 200W LED Warm AC or DC White RGB Spotlight Flood Light Garden | eBay

I'm linking to the ebay seller, whom I had a good luck with. I received a partially broken LED at first, but they immediately sent me another working one without any troubles.
 
Thank you Naoki. This is all very valuable to me and it saves me quite a bit of time. I will have to save this post for my next enclosure.
 
Chad, it does generate a bit of heat (I think you grow some nice cool-growers). I don't know how to measure it, but the heat sink was going warmer when I stopped the fan. I would prefer passive cooling (no noise). But the efficiency of LED drops with the temperature, so people seems to think slight energy loss due to active cooling is compensated by the increase in the efficiency.

Angela, it is not a easy question, I think. The efficiency of LED seems to be highly variable among different fixtures (depending on their design). I would "guess" that this cheap LED has similar operating cost (PPF efficiency, i.e. efficiency relevant for photosynthesis) as T5HO. More expensive ones (Vero or Cree CXA) are likely to be more efficient than T5HO. For photosynthesis efficiency, HPS and MH is highly cost effective (much better than T5HO). Some of the top-end LEDs are now better than HPS and MH in terms of operating cost.

Table 2 in 2nd page of this document has a comparison of LED vs HPS vs MH. The two blue columns in the table are the relevant numbers (high PPF efficiency value is better).
 
LED lights are very efficient as long as you remember that they were
created for high light level plants like "medicinal plants" and (for some
reason) lettuces...
 
Alla, maybe I'm not using the correct terminology. When you are attaching the CPU to heatsink, you use the gray stuff, which can conduct heat between the CPU and heatsink. Even though the surface is supposed to be flat, there could be some small irregularity, so the heat conductive grease is avoiding the air pocket. There are some thermal grease with adhesive property, too. I drilled holes, used a tap, and attached the LED with machine screws. But if you use the adhesive type, you can just glue the LED to the heatsink.

Have you had a chance to assemble your DIY LED yet?

Silvan, take a look at the link I gave in message #4. The test shows amazing variation. Even though all of the tested LED fixtures are considered to be "high-end", one of them gives 0.84 micromoles/s/W while a better one gives 1.60 micro moles/s/W. A lot of the LED makers use marketing hypes, but this data tells me that we should be careful.
 
I received the diodes from China, but I haven't had the chance to do anything with them yet. Keep in mind, my goals are as much aesthetic as functional, so until I find an attractive heat sink to attach them to, I won't start on them. I'm looking at aluminum foam as a mounting substrate, just a matter of contacting the manufacturer and getting it in the right shapes and sizes.

I will need to use an adhesive thermal conductor, as these diodes will be suspended. How would you isolate the soldered leads from the heat sink - shrink tubing?
 
Well all the info provided in the link seems very interesting,
but I don't really have the intellectual capacities to understand
all of it..lol
I just wanted to warn people not to start with priced plants (orchids)
without knowing their light requirements as I did with my phrags.

kovachii before LED :

g4ia.jpg


kovachii after LED:

kxc2.jpg
 
and it's not the worst looking plant..
Keep a close watch on your plants, because it took about
a month period to go from picture 1 to picture 2. :)
Now my phrags used for this experiment are at 4feet under my fixture
at a 12 hours light cycle. The bleaching and burning seems to have stopped.
But they aren't getting better either.
 
ALToronto said:
I received the diodes from China, but I haven't had the chance to do anything with them yet. Keep in mind, my goals are as much aesthetic as functional, so until I find an attractive heat sink to attach them to, I won't start on them. I'm looking at aluminum foam as a mounting substrate, just a matter of contacting the manufacturer and getting it in the right shapes and sizes.

I will need to use an adhesive thermal conductor, as these diodes will be suspended. How would you isolate the soldered leads from the heat sink - shrink tubing?
Click to expand...

I'm using a twist-tie to make it stay to the side of the heatsink. Are you talking about the insulating against the heat? The heat sink doesn't become too hot. For electrically insulating the soldering point on the LED array, I might use the liquid tape, but I probably leave it as is.

Silvan, that's too bad. Which model of LED fixture are you using? With the white LED, I can easily tell the appropriate distance. But with R+B type, I wasn't sure at first. I did have tiny amount of bleaching (with 90W R+B), too, but I caught early on. But in general, I feel like that plants become greener with R+B (just anecdotal) if not too intense.
 
well, I don't want to hijack your thread. I just wanted to warn people
not to use valuable plants for the experiment as I did.. :)

the biggest one is running at half capacity as ideally it would
need to be at least 6 feet above the folliage and the ceilling in my
basement isn't high enough ... :eek:
 
Last edited:
naoki said:
Alla, maybe I'm not using the correct terminology. When you are attaching the CPU to heatsink, you use the gray stuff, which can conduct heat between the CPU and heatsink. Even though the surface is supposed to be flat, there could be some small irregularity, so the heat conductive grease is avoiding the air pocket. There are some thermal grease with adhesive property, too. I drilled holes, used a tap, and attached the LED with machine screws. But if you use the adhesive type, you can just glue the LED to the heatsink.
Click to expand...
Thermal grease is a term people use; if you want to be more precise then Thermal Interface Compound is a better term. I use Arctic Silver Ceramique 2:
http://www.arcticsilver.com/cmq2.html
it is a white colored paste. I started using the grey colored, silver filled, Arctic Silver 5 but it is so tenacious that I had to be very careful to not leave grey smudges all over the house.

The pastes work much better than the tapes. If you need an adhesive material then the two component epoxy thermal compounds would be better than tape.
http://www.arcticsilver.com/ta.htm
 
No worry of 'hijack', it's great to hear your experience, Silvan! Those seem to be pretty nice (and expensive) models. It looks similar to Bysen, but it is backed up with good warranty, and quality diodes (Cree+Bridelux, I don't think Bysen uses Cree+Bridelux). Yes, with 480W (actual), you can easily bleach orchids! For Paphs, I'm getting decent growth with 12 W/sqft.

Thank you for the recommendation, David! I used left-over grease from assembling computers. I'll get the one you recommended.
 
Cree CXA-3070 is amazing!

A bit of update:

Wow, there is no comparison between Cree vs ebay cheap LEDs. Cree CXA3070 is one of the cutting-edge white LEDs at this moment. Compared to ebay COB LEDs, CXA3070 is putting out about 60% more light per watt!!! Most of us are happy with whatever we have been using until we see the difference since we don't know what's out there.

OK, here is the punch line. CXA3070 is $40+$2.23 for holder, and 100W ebay LED is $8. So Cree is 5 times more expensive initially. But after running it 1.04 years, Cree becomes cheaper (I'm using $0.19497/kWh, which is probably higher than most of you). So it doesn't make sense to get the cheap LEDs. I started this thread with the cheap ebay LED. But now, I would recommend Cree CXA3070 over ebay LED. It's difficult to compare against florescent light (or red+blue type LED grow light). But I'm guessing that this CXA3070 is one of the most cost effective ways to grow with artificial lighting. The total costs is about $60 per 50W module of CXA3070 (pretty comparable initial cost to T5HO). You can drive it at a higher wattage (e.g. 100W), but I didn't want to push it to the maximum capacity.

Materials
  1. LED:
    CXA3070 (3000K) comes in 3 grades (bins) depending on the efficiency: Z4 (most efficient), Z2, Y4 (least efficient). Mine is the middle bin (Z2). The LED holder is a bit tedious to use (drill holes to the heatsink), but you don't have to solder/glue the LED.

    Here is the CXA3070 + holder:


    Comparison of the size:

    Clockwise from top left: Cree CXA-3070 (3000K, middle bin; Z2), ebay "100W" Warm White (around 3000K), ebay "100W" Cool White (around 6000K), ebay "30W" Warm White (around 3000K)

  2. Drivers: I had 3 kinds of constant current drivers, all from ebay:

    From top to bottom: 50W (1.5A), 30W (1.05A), 20W (0.6A).

  3. Heatsinks: whatever CPU heatsink with a fan.

    From Left to Right: Cree CXA3070, 3000K, ebay "100W" Warm White, ebay "100W" Daylight White, ebay "30W" Warm White.
  4. Wire: Cerrowire 18-2 Thermostat Wire (18 gauge, 210-1002BR from HomeDepot).
  5. Thermal paste: Arctic Silver Ceramique 2

Measurement:
Explanation of the data columns:
  • "fc.1ft": I placed a light meter 12" away from the emitter, aligned to the center of the emitter. It was measured after running it for a minute or more (to stabilize the temperature).
  • "input.W": watt used by LED + driver. This was measured by kill-a-watt meter.
  • "Vf": forward voltage, the voltage across the + and - or the LED (unit: V)
  • "current.A": current going through the LED (unit: A)
  • "LED.W": watt used by LED (excluding driver). This is Vf * current.A
  • Drvr.Effic: Driver efficiency. (=LED.W/input.W)
  • fc.per.inW: footcandle at 12" per given input watt (=fc.1ft/input.W)
  • fc.per.LEDW: footcandle at 12" per given input watt (exclude power loss due to driver) (=fc.1ft/LED.W)

Code: 
LED        Driver     fc.1ft input.W    Vf current.A LED.W Drvr.Effic fc.per.inW fc.per.LEDW
CXA3070    20W(0.6A)     520    19.0 33.58     0.469 15.75      0.829       27.4        33.0
CXA3070    30W(1.05A)    970    33.8 35.04     0.864 30.27      0.896       28.7        32.0
CXA3070    50W(1.5A)    1500    59.0 37.03     1.427 52.84      0.896       25.4        28.4
ebay-100W  20W(0.6A)     320    18.8 27.51     0.552 15.19      0.808       17.0        21.1
ebay-100W  30W(1.05A)    480    27.2 28.06     0.866 24.30      0.893       17.6        19.8
ebay-100W  50W(1.5A)     730    46.0 28.81     1.425 41.05      0.892       15.9        17.8
ebay-30W   30W(1.05A)    520    30.1 31.01     0.866 26.85      0.892       17.3        19.4

LED on the left, and lightmeter on thr right:


Results (graphical representation):


Notes:
  • With regard to the driver efficiency, those cheap ebay drivers (30W and 50W) are pretty good (89% efficiency). But the 20W driver is not great (around 82%).
  • When you look at fc.perLEDW, you notice that efficiency of Cree and ebay LED increases with lower current. I think some other people calculated that radiometric efficacy of this Cree can be >40% with 20W (0.6A) driver. In other words, 40% of electic enegy can be converted to light energy (the rest is wasted as heat).
  • However, running Cree CXA3070 at lower current is a false economy. You can run 2x CXA3070 @50W, or 3x CXA3070 @30W to get the similar amount of light. But it takes 10.7 years to make the cost (initial + electricity) even (13h/day). So I'm going to run it with 50W driver
  • As mentioned earlier, after 1.04 years (13h/day), Cree CXA3070 becomes cheaper than ebay LED.
  • I was a bit surprised, that luminous efficiency of the 30W ebay LED isn't so different from 100W ebay LED.

These measurements are approximate. For example, the color spectra could be slightly different even though both Cree and ebay LEDs are warm white (around 3000K), and I used footcandle instead of PPF of PAR. Additionally, the light spread could be slightly different and 1-point measrement at the center may be misleading (I think the light spread looks similar).
 
Last edited:
Spectral difference between Cree vs cheap ebay? Since ebay LED doesn't have data sheet, I guess we need a spec photometer. I have been considering this DIY spectrometer, but I haven't done it yet. Has anyone played with this $40 spec.? Eventually, I might be able to compare PPFD of PAR, though. It's a bit tedious, and I haven't had time to do so. When I get around, I'll post the data (but not any time soon, though).
 
naoki said:
Spectral difference between Cree vs cheap ebay? Since ebay LED doesn't have data sheet, I guess we need a spec photometer. I have been considering this DIY spectrometer, but I haven't done it yet. Has anyone played with this $40 spec.? Eventually, I might be able to compare PPFD of PAR, though. It's a bit tedious, and I haven't had time to do so. When I get around, I'll post the data (but not any time soon, though).
Click to expand...

I can't find a link to the detailed step-by-step construction.
 

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