# Most efficient white led at low current?



## fnj (Jan 26, 2011)

What is the most efficient white LED available at a current level of around 0.26 ma?


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## J_C (Jul 7, 2011)

Perhaps you mean 26mA or 0.26A?? If you really mean 0.26mA I don't see the point in finding one but I'm always glad to learn.


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## fnj (Sep 14, 2011)

I mean 0.26 ma. With a Radio Shack 276-0017 that gives me a dandy night light. I even tried an XM-L (!) at 0.26 ma and the performance is dandy. I just wondered if there was something else even better.


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## deadrx7conv (Sep 14, 2011)

Repeat of what JC said. 

What driver or battery did you use to get .26ma? What lumen output? 

Typically, 5mm LEDs run at 20ma(notice the missing decimal) or .020A 

Reminds me of a phone bill:
http://youtu.be/D2isSJKntbg


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## Curt R (Sep 14, 2011)

I am not sure that you can get visible light out of an LED with only
1/4 of a mA drive. 

How are you measuring the current draw to the LED?

Curt


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## Lynx_Arc (Sep 14, 2011)

Curt R said:


> I am not sure that you can get visible light out of an LED with only
> 1/4 of a mA drive.
> 
> How are you measuring the current draw to the LED?
> ...


 newer high end brand LEDs can give out usable light down to 0.1ma. The trick is having a reflector and night adjusted eyes. You should try direct driving an LED off 2 nimh batteries and see how long and low it goes before unusable.


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## J_C (Sep 14, 2011)

Whether an LED needs 0.26mA or slightly more is pretty irrelevant. You win no prize for small fractions of a mA, nor do you even save power when using power to post and us to reply. Seeking some exotic part for this purpose does not seem logical nor beneficial in any way.


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## deadrx7conv (Sep 14, 2011)

http://www.candlepowerforums.com/vb/showthread.php?89607-White-LED-lumen-testing This thread is a good read. You might find your answer. I'd wager that you'd want the smallest LED that you can find since efficiency below 10ma is lame for larger LEDs. Seems they need some power to light the whole die and start working. You should look for some 3mm or 5mm LEDs from Nichia, The Shack, Cree... Go small as possible for that 1/4 ma of power.


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## IMSabbel (Sep 15, 2011)

Like the others said, pointless.

At this drive current, driver losses will dominate everything else (especially if your way to reach those low currents is just a series resistor)


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## MikeAusC (Sep 15, 2011)

For high power LEDs, it's well known that as you increase current, the efficiency decreases. Well it turns out that at very low currents, the efficiency also drops off - so there's a point of maximum efficiency.

For the XR-E that peak was at 50mA - about 1/20th of the maximum current - with a sharp dropoff in efficiency below that current.

So for a 20mA LED you could assume it's most efficient around 1mA.


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