XM-L U3???

[mr.lumen]

why do most light set ups drive them at 3amps? what can they handle and how much more output do you get at 5 as opposed to 3?

5 amps

(5 watts is not overdriving)

 

[monkeyboy]

why do most light set ups drive them at 3amps? what can they handle and how much more output do you get at 5 as opposed to 3?

It depends entirely on the heatsinking. Cree states 3A maximum drive level. There's a thread somewhere here on cpf where someone soldered an xm-l directly to a copper block and found that output continues to increase up to about 5.5A compared to about 4A with a regular pcb.
Obviously lifetime will be significantly reduced with overdriving at 5A but I've run it continuously and no angry blue so far.

 

[CarpentryHero]

Mine arrived three days ago, I'll try and put power to them some how in a couple days when I meet up with my friend that knows how too solder

 

[lampeDépêche]

5 amps

(5 watts is not overdriving)

So a straight-line rule with 320 lumens/350 mA would give you about 4500 lumens at 5A, but I'm assuming that you're not getting 4500 lumens from a single XML, even a U3. So what am I missing? It must not be a straight-line rule, i.e. the efficiency must drop under higher currents.

So what kind of output *do* you think you're getting on 5A?

And if my math is just totally barking up the wrong tree, then forgive me--I'm totally ignorant about electronics. (But curious!)

 

[twl]

So a straight-line rule with 320 lumens/350 mA would give you about 4500 lumens at 5A, but I'm assuming that you're not getting 4500 lumens from a single XML, even a U3. So what am I missing? It must not be a straight-line rule, i.e. the efficiency must drop under higher currents.

So what kind of output *do* you think you're getting on 5A?

And if my math is just totally barking up the wrong tree, then forgive me--I'm totally ignorant about electronics. (But curious!)

The efficiency DOES drop with higher currents.
The more current you put in, the hotter it gets inside, and the worse the efficiency gets, leading you to put more current in, and at some point it just burns up.
Some people just have to learn the hard way. If it really worked, there wouldn't be any limit to the current, and all the companies would be doing it.

 

[mr.lumen]

awesome.

Mine arrived three days ago, I'll try and put power to them some how in a couple days when I meet up with my friend that knows how too solder

 

[monkeyboy]

So a straight-line rule with 320 lumens/350 mA would give you about 4500 lumens at 5A, but I'm assuming that you're not getting 4500 lumens from a single XML, even a U3. So what am I missing? It must not be a straight-line rule, i.e. the efficiency must drop under higher currents.

So what kind of output *do* you think you're getting on 5A?

And if my math is just totally barking up the wrong tree, then forgive me--I'm totally ignorant about electronics. (But curious!)

If only that were true!
the u3 bin is 320 - 340lm at 700mA
yes, efficiency drops at higher drive levels. Probably only getting around 1500lm at 5A.

 

[Atakdog]

i just got off Crelant's website. they are advertising a coming 7G5CS U3 with 920 lumens compared to their U2 model's 895.

 

[lampeDépêche]

... 920 lumens compared to their U2 model's 895.

and 25 out of 900 is a bit less than 3%. All improvements are good, of course.

 

[moozooh]

If those 3% come with an improvement in tint and/or color rendition, it's worth the change. But at this point I'd rather wait for XM-L2 and lights designed with its improved power efficiency in mind.

 

[HighlanderNorth]

If those 3% come with an improvement in tint and/or color rendition, it's worth the change. But at this point I'd rather wait for XM-L2 and lights designed with its improved power efficiency in mind.

I'm just going to wait for the XM-L3 U5.... Or the next Cree LED, the XN-L.

 

[moozooh]

Jokes aside, the XM-L is Cree's most efficient LED to date, and it's over two year old; it is most logical that it's the next in line for an update to their new Si3 platform, and as far as I know, the only single-die one left. I'm just saying that simply getting a miniscule improvement in brightness isn't going to be noticeable no matter how you put it, while an improvement in runtime on any mode is always welcome. Arguably more welcome that increased brightness on lower modes...