cheap ebay DIY LED

[naoki]

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. The one in the photo is not a good one, neither; it wastes a bit of energy. 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

I measured the efficiency of the AC/DC driver. After warming up, forward voltage is 31.01V, and it was drawing 866mA of DC. From the AC side, it was consuming 30.1W (measured with kill-a-watt). So the efficiency is 0.866 * 31.01 / 30.1 = 0.891. 89% efficiency for the driver isn't so bad for the price.



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.

It is difficult to compare with linear florescent bulbs, but here is my measurements of T5HO. But this is 6500k T5HO (not warm white, which usually registers lower fc values for a given watt).

AnonYMouse measured household LED. If you divide the fc@6" values by 4, you get approximate fc at 12".

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.

[zxyqu]

Interesting post here Naoki. I'll check it out.

[larrylwill]

Naoki: Have you looked into those red/blue leds. I would really like to see the color spectrum of the warm white 3500k vrs the cold white 6500k leds. Have you tried the leds on your orchids? Results?

[naoki]

Larry, I've been using Red/Blue LEDs over 1.5 years. They work, and orchids grow/flower well. My R+B fixures aren't the high-power one, so I use them for lower light Paphs and Phals.

For human eyes, warm white LED looks similar to warm white fluorescent bulbs (and 6500K LED looks like 6500K T5HO/CFL).

I haven't put this COB LED on orchids yet. If you are wondering if white LED works or not, I have been using Cree LED bulbs from HomeDepot (4x 9/9.5W bulbs for 3 sqft area), and they seem to work OK (but I've been using them only 6 months, so it could be too short to tell anything).

I've recently learned that if you drive the high power COB LED at a lower current, you can gain quite a bit of efficiency. For example, here is a table of Cree CXA. CXA3070 can take up to 117W, but you can increase the efficiency by using lower current (700mA or so, which results in 30W). Maybe this applies to the cheap ebay LEDs, too. So I should have gotten the LEDs with higher capacity.

[larrylwill]

Naoik:
Right now Im using the florescent and want to change to leds. I can bloom the Phals with the window light in fact they are on the top shelf above the lights. Its the Cats and Ocs I'm trying to bloom. I'm an electronics engineer so I can follow your posts. I would be willing to buy a couple of those Chinese leds to try with some Oncs and Cats but It takes a year to really tell if they will bloom. Its a painfully slow process. I wouldn't mind keeping in touch with you by email. I will send you my email address in a pm.

[naoki]

That's great you are electronics engineer! Yes, we'll keep in touch. I'm slowly learning about electronics, but a lot of things are beyond my understandings.

My concern with the ebay LED is the durability. So I should start using it to test the durability, but I haven't had time to set it up. My older R+B panel is crappy, and I have to keep replacing the blue LEDs every couple months.

I don't grow lots of high light orchids, but I can get some rupicolous Laelia's grow and flower under T5HO (about 6-10" between the bulb and the top of the leaves, getting 1000fc or so, no natural light). So if you place Catts and Oncs close enough, they should get enough light.

[trdyl]

Thanks for posting this naoki!

These look like they'd be perfect for a small shelf.

[larrylwill]

I purchased a 50W module last night for under $8 shipped. Soft White.

[larrylwill]

Got my 50W led today. Hows that heat sink working over hours. Do you have a fan on it or can it be run without it? I should get time to try it this week.

[naoki]

Cool, Larry! I just added the efficiency of the driver (89%) to the original post.

Without the fan, it was warming up quite a bit (which results in the reduced efficiency). I tried to measure the temp with IR thermometer, but my IR thermometer doesn't seem to work well with the shiny metal surface. With a little bit of active cooling, the temp is kept pretty low (slightly warm by touching). 3.5V was enough, but I'm using a newer, more efficient AC/DC converter with 5V now. Some people run these big LED's with passive cooling, but they use a big, expensive heatsink.