xml output ?

Hi, i would like to know what sort of output i will be looking at if running a XM-L T6 at 1.25 Amps ?
thanks
Ant

472 emitter lumens.

damn, no really ? how did you work that out ? thanks !

Here is a link to the amps vs output percent on page 5 : http://www.cree.com/products/pdf/XLampXM-L.pdf

At .7 amps the XM-l T6 is 100% which is 280 lumens min.
At 1.25 amps the XM-L T6 is about 162% which is about 450 lumens!

Of course, general rules in a flashlight with a reflector you would lose 30% so your OTF lumens in a FL would be around 315 lumens

thankyou for that, its very helpful.
the reason i ask is i have ordered a new LED for my NEX and im wondering what the outcome might be !

Wow.

So which is the current 1xAA xml to get, without a strobe?

zs&tas said:

damn, no really ? how did you work that out ? thanks !

Click to expand...

Register here and you will get detailed data about Cree LEDs:
http://pct.cree.com/

rajalexi said:

Here is a link to the amps vs output percent on page 5 : http://www.cree.com/products/pdf/XLampXM-L.pdf

At .7 amps the XM-l T6 is 100% which is 280 lumens min.
At 1.25 amps the XM-L T6 is about 162% which is about 450 lumens!

Of course, general rules in a flashlight with a reflector you would lose 30% so your OTF lumens in a FL would be around 315 lumens

Click to expand...

As a general rule of thumb, emitter efficiency drops as input current rises, so, these numbers will probably be a bit optimistic. I'd guess that you'd get around 440 emitter lumens at 1.25A, but, that also depends on the characteristics of the emitter itself. I know, nitpicking. I just thought that someone reading this might think that an XM-L making 280 lumens at 0.7A will make 1120 lumens at 2.8A when, in reality, it will make more like 900 lumens at 2.8A.

jirik_cz said:

Register here and you will get detailed data about Cree LEDs:
http://pct.cree.com/

Click to expand...

cool tool...
thanks!

PCC said:

As a general rule of thumb, emitter efficiency drops as input current rises, so, these numbers will probably be a bit optimistic. I'd guess that you'd get around 440 emitter lumens at 1.25A, but, that also depends on the characteristics of the emitter itself. I know, nitpicking. I just thought that someone reading this might think that an XM-L making 280 lumens at 0.7A will make 1120 lumens at 2.8A when, in reality, it will make more like 900 lumens at 2.8A.

Click to expand...

PCC said:

As a general rule of thumb, emitter efficiency drops as input current rises, so, these numbers will probably be a bit optimistic. I'd guess that you'd get around 440 emitter lumens at 1.25A, but, that also depends on the characteristics of the emitter itself. I know, nitpicking. I just thought that someone reading this might think that an XM-L making 280 lumens at 0.7A will make 1120 lumens at 2.8A when, in reality, it will make more like 900 lumens at 2.8A.

Click to expand...

But in the data sheet you can look up the "Relative Luminous Flux vs. Forward Current" plot on page 5, and take the output percentage from there, where the efficiency drop should be included.
At 2.8A, the graph seems to be at about 310% (of 280 Lumens), which is 868 Lumens. So all the info one needs should be in the data sheet, no need for "rule of thumb" calculation efficiency-wise.
(Well, for the reflector loss for OTF Lumens maybe )

Moving this to LED...

Keep in mind the output curve is for a junction temp of 25C. The output is derated as the temp goes up (down 28% at 700mA at max rated 150C). So your output will be dependent on your existing heat sink as well.

PCC said:

I'd guess that you'd get around 440 emitter lumens at 1.25A

Click to expand...

Don't guess, use the Cree product characterization tool linked above...

"Of course, general rules in a flashlight with a reflector you would lose 30% so your OTF lumens in a FL would be around 315 lumens"

Can't seem to figure this one out. I have a 60 degree reflector by Khatod on a led and I GAIN around 50% MORE lumens when I measure the brightness off a white wall. How can you calculate that minus 30% when in fact I GAIN brightness. When I use a 20 degree reflector then I really gain a lot more, granted the beam angle is reduced. After all who uses a bare led all by itself with a 125 dergree spread? What you are saying is that you lose brightness by using a reflector. I must have a magic reflector.

Your reflector is not magical, your measurement methods are being confused. The output of the LED will be measured in Lumens, the light projected on the wall will be in lux. The reflector will focus the wide angle light from the LED and place more of it on the target. In total some of it will be lost. Because the light is focused into a smaller area it will apprear to be brighter to the eye as well.

thanks for all the input guys, still waiting for the LED, seems like its guna be a good upgrade though ! My NEX is by far my fav light, i think there awsome size/design wise. another quick question, do you think there is a heat difference between the current Q5 and the XML at 1.25 amps, is the XML cooler as it is more effiecent, or hotter as its brighter ?

jirik_cz said:

Don't guess, use the Cree product characterization tool linked above...

Click to expand...

Not everyone has access to the data sheets and, sometimes, you just want a quick estimation. I just didn't want people to think that you can simply triple or quadruple the lumens number when you triple or quadruple the input current. It doesn't work that way.