Overdriving CREE LEDs

[bevansmw]

I noticed that some people drive the CREE LEDs more to the tune of around 1.2A to get more lumens out of them. Reading the data sheets for CREE XR-E, XP-E and XP-G shows max current for the more common bins found and used in the modified dive lights to be 1A. I also saw the potential damage from over-driven LEDs in CREEs data file for the LEDs, one picture showing a burned LED wire and the other a burn on the LED chip.

Having said that I'm curious if anyone has experience driving these LEDs above 1A, say an XR-E R2 to the tune of 1A-1.2A to get more lumens out of it. If so whats your experience with the life of the LEDs when they're overdriven? Will they still last a significant amount of time or do they rapidly burn up? In other words approx how long will the LED last when driven between 1-1.2A.

I noticed DE and KD both make drivers to provide around this amount of current through the CREE LEDs, anyone with some experience using them?

 

[Packhorse]

Dont believe what DX and KD say in the specs.


As for over driving LED's.... If done correctly with lots of heat sinking you will probably be fine.
I over drive my 4 XR-E Q5 LEDs at 1400ma each in my can light.
The reason I do it is because with my choice of driver I can either choose 700ma or 1400ma. Well actually its 2800ma/4 (4 LEDs in parallel) or 2800ma/2 (2 paralled pairs of LEDs wired serried).
Its not twice as bright but it does only run half as long.

LED's are not like halogens. With halogens the more you over drive them the more efficient they are. LEDs get worse when over driven.

I have another light that I built using a Cree MC-E LED and I chose to run that at half power. Once again its more than half as bright and runs for twice as long.
Its output is comparable to a 10w HID and it runs for 3 hours. Not bad for a hand held.

 

[bevansmw]

Thanks, I noticed a lot of people on DX and KD complain about the specs constantly being wrong and often the drivers will have reviews where people have measured the actual output from the driver they received so I did figure the drop-ins that they sell are probably not driven to full potential.

I bought one of the XP-G R5 drop-ins I just saw on KD today and a driver for my XR-E R2 to bring it to 3 modes and approx 1.1A per the review it had, supposed to be 1.2A driver per KD specs. Suppose I'll be happy with a full 1A since the heatsinking isn't the best in the SL4 plastic case.

 

[wquiles]

I am with Packhorse on this one. With proper heatsinking, overdriving is not too bad, and many of us at the flashaholic forums do it routinely, but it all depends on how much overdrive, and the temperatures which the LED will see. If you look at the data sheet for the XP-G you will see that it is rated output was measured at a laboratory controlled temperature of 25C. You will also see in the data sheet that as the junction temperature of the die increases past 25C, the output drops in a very linear fashion - my point, unless you can keep the overdriven LED relatively cool, you are actually loosing lumens the more you overdrive the LED - the key as Packhorse mentions is to find that happy medium of "reasonable" overdrive with a good heatsink in order to have reasonable life expectancy for the LED.

Lastly, keep in mind, that even with a perfect heatsink of infinite capacity, you can still kill an LED when overdriving it if the current is high enough to melt the extremely fine gold wires that tie the package to the die - that is how you know you pushed the LED too hard

Will

 

[haibeis]

hey Bevansmw - ya beat me to it again!

can you show some beam comparisons between the XRE and XPG when you get it done?

cheers,

 

[bevansmw]

hey Bevansmw - ya beat me to it again!

can you show some beam comparisons between the XRE and XPG when you get it done?

cheers,

Sure can, I have to wait for it to arrive though. Saw it when I was looking at drivers and couldn't help it so I pulled the trigger.

I bought two of the 35mm x 28mm reflectors at the same time so I can move the R2 bits to those ones and be able to close the SL4's all of the way and not mash in the batts.

@wquiles

Thanks, I was looking at the spec sheets for the LEDs and noticed the non-linear raise in lumens as the current increases as well as the drop in lumens as temp increases past 25 C (only 77F).

 

[Packhorse]

Lastly, keep in mind, that even with a perfect heatsink of infinite capacity, you can still kill an LED when overdriving it if the current is high enough to melt the extremely fine gold wires that tie the package to the die - that is how you know you pushed the LED too hard

Will

In other words, push it until it blows then back it off slightly.

In my limited experiance with the XP-G vs XR-E I found the XPG brighter but with a bigger hot spot. This is probably more to do with the fact the reflector I used was designed for a XR-E and a dedicated XP-G reflector could very well produce a tighter spot.
As fas as use of XP-G's with aspheric lenses I find them quite disapointing due to the wider dispersion angle of 125 deg vs 90 for the XR-E.