# Most Efficient White LED



## Agator007 (Jun 29, 2011)

I am wondering who makes the most efficient (lumen/watt) white LED for high power applications?

I've used the SST-90 in my spot-lights, but would like to make a smaller more efficient flashlight and/or a flood light and am wondering if I can get more lumens for the battery by using Crees instead.

Cree has so many white LED products it's a little confusing, but I saw this:

http://www.dealextreme.com/p/ultraf...-flashlight-w-strap-1-x-18650-1-x-17670-90775

And am wondering if the CREE can actually produce 1000 to 1200 lumens at 3 A, and what appears to be about 3.2 V

Where as the SST-90 typically produces 2200 lumens at 9 A and 3.5 V.

Also, are there any other LED brands that are comparable in efficiency and power?

Thanks


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## shao.fu.tzer (Jun 29, 2011)

Since no one is fielding this one, I guess I will. I would have to say Cree is currently the leader (someone correct me if I'm wrong) with their XM-L and XP-G LEDs... Any of the XM-L bins available at the moment can't produce 1000 to 1200 lumens @ 3A. Maybe in the near future... If size isn't a matter, try wiring a ton of XP-Gs or XM-Ls together...


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## deadrx7conv (Jun 29, 2011)

Shao is right. If there is room, you could run several LEDs for that lm/w efficiency. 7 XPG's(or Rebels, P4's,...) or 4-6 XML's, bin dependent, at 1.5-2.5w each for a total of ~10w should be close to that magical 1000lm. You might even be able to pull it off with 2-4 SST50, MC-E, or P7.... 

Another option is simply to run the SST90 at 3A. If you get a top bin SST90, you could possibly be in the 900+ lm range with 3A! 

I think that big LEDs like bridgelux, citizen, sharp, ledengine, edison.... can also be underdriven and get you that magic lm/w efficiency too.


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## Agator007 (Jun 29, 2011)

Thank you for the comments. I've been looking at a lot of spec sheets for both luminus and cree, and it seems that the crees are relatively more efficient at any point on the IV curve compared to the luminus at it's respective point. The Cree also has a lower Vf at its max current (3.2 vs 3.5)

The XM-L data sheet claims to have a thermal conductivity from the junction to (not sure--the heat sink?) of 2.5 C/W, which is just a little more than the SST-90 (something like 2.15). 

Based on the data sheet it seems like the XM-L is rated pretty conservatively and possibly capable of being run at 5 or more amps with cool junction and a reasonable quantum efficiency.

But at least with the SST-90, its still the brightest overall and actually puts out a true 2250 lumen. (The dealextreme light just seems a little too good to be producing 1200 lumens at only 3A)

I just ordered a couple of cool white XM-Ls at the highest available efficiency bin, which was 290 lumen at 0.7A and 947 lumen at 3A.

Thanks again.


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## CKOD (Jun 30, 2011)

Agator007 said:


> Thank you for the comments. I've been looking at a lot of spec sheets for both luminus and cree, and it seems that the crees are relatively more efficient at any point on the IV curve compared to the luminus at it's respective point. The Cree also has a lower Vf at its max current (3.2 vs 3.5)
> 
> The XM-L data sheet claims to have a thermal conductivity from the junction to (not sure--the heat sink?) of 2.5 C/W, which is just a little more than the SST-90 (something like 2.15).
> 
> ...



Youre right on, people have done 4.5-5A overdrives with XM-Ls and they will take it if you can cool it. However MCPCBs vary a lot, so if you want to run one extra hard like that, its either soldering it to a copper slug directly, or finding a good MCPCB. Check out http://pct.cree.com (free registration, make sure you save the email with the link to access it) if you want to see actual numbers and not just estimate off curves, though they dont go outside the stated limits. 

The XM-L has the highest efficiency of power LEDs at the moment. Most of cree's multi-die stuff look like it uses what looks like the same die as the XP-E and XR-E (Could be wrong) so the efficiencys are about the same.


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## deadrx7conv (Jun 30, 2011)

http://www.candlepowerforums.com/vb/showthread.php?308569-No-real-benefits-to-overdriving-XML

http://www.candlepowerforums.com/vb...tartup-when-overdriven-to-4A-(in-rush-current-)


http://www.candlepowerforums.com/vb/showthread.php?316844-XML-runs-hotter-than-MCE-...-why


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## Agator007 (Jul 1, 2011)

CKOD said:


> Youre right on, people have done 4.5-5A overdrives with XM-Ls and they will take it if you can cool it. However MCPCBs vary a lot, so if you want to run one extra hard like that, its either soldering it to a copper slug directly, or finding a good MCPCB.


 
I don't know what an MCPCB is, but I do use copper plates to mount the LED.

I destroyed an SST-90 once without attaching it to copper--but directly to aluminum.

Those links are very interesting, it looks like the LED must be encountering a saturation of the recombination region over 3.5A. So it has the opposite problem of the SST-90, which seems to be limited by heat transfer from the junction where the XM-L has plenty of cooling capability.


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## CKOD (Jul 1, 2011)

Agator007 said:


> I don't know what an MCPCB is, but I do use copper plates to mount the LED.
> 
> I destroyed an SST-90 once without attaching it to copper--but directly to aluminum.
> 
> Those links are very interesting, it looks like the LED must be encountering a saturation of the recombination region over 3.5A. So it has the opposite problem of the SST-90, which seems to be limited by heat transfer from the junction where the XM-L has plenty of cooling capability.


 

Metal Core PCB. The "Stars" or various shape aluminum circuit boards that LEDs are typically put on for production items.


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## Curt R (Jul 1, 2011)

If you take 8 XPG LEDs and drive them at 350 mA each to equal
about 3 Amps total, the output will be about 1150 Lumens in a 
bare bulb condition. However the Out The Front Lumens will be
closer to 850. In laboratory conditions Cree has exceeded 200
Lumens per watt, we just have to wait about two more years for
production parts. Our first production lights using the Luxeon I
LED produced an amazing 25 Lumens! 200 Lumens with 8 LEDs.

With 30 XPG LEDs each driven at 100 mA each, the output is then 
about 1300 Lumens in the bare bulb condition, or 950 OTF. Just
not practical from a cost point.

What we have been describing is all of the LEDs in parallel. If we put 10 XPGs
is series and drive the string at 350 mA we have 1400 lumens. And eight
strings would give us our 3 Amps of drive current and 11,000 Lumens. 

I think I need to get some sleep.

Curt


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