XML T6 vs. U2

[DellSuperman]

Thanks for the reply kitty. Ok, so what does it mean that 700ma is 100%? Does this mean what it is designed for and everything above this needs either active or passive cooling?

EDIT, after reading the datasheet again, I am going to guess its about 225-250 lumen or abouts at 600ma. I will check my math later but I think this will work for what I want.

Thanks hellokitty

Driving it at 700ma is at 100%.
Anything higher is overdriving & you definitely need cooling measures because a T6 at 2000ma or higher is gonna generate alot of heat.

Sent from my HTC One X using Tapatalk 2

 

[SkOrPn]

Any reason you must have an XM-L for such a low current? Maybe an XM-L2 if your stuck on XM-Ls

Yes, I was specifically looking for a LED that would provide as much efficiency as possible and I was not aware of the XML2 until after I purchased the XML U2, lol. If I find a good deal on the XML2 I will go that route.

 

[Justin Case]

By 100%, are you referring to the relative luminous flux? The XM-L lumens rating is given as the output at 700mA drive current. For a T6 flux bin, the rating is 280 lumens when driven at 700mA. To calculate lumens output at other drive currents, you refer to the graph of relative luminous flux vs. forward current. As you can see from that graph, at 700mA, the relative luminous flux by definition is 100%, which means that to calculate the output at 700mA, you multiply 280 lumens by 100% to get ... 280 lumens.

Driving an XM-L at greater than 700mA is NOT overdriving the LED. The datasheet spec clearly states that the max forward current rating is 3000mA. What percentages greater than 100% mean is that for forward currents greater than 700mA, the output is greater than 280 luimens, which should not be any surprise.

So, for example, if you drove an XM-L T6 at the max of 3000mA, the relative luminous flux is about 325%. Thus, the calculated output at that drive current is 280 * 3.25 = 910 lumens.

At the other end, if you drove the XM-L at say 600 mA, the relative luminous flux looks like it is halfway between 75% and 100%, or about 87.5%. So the calculated output is 280 * 0.875 = 245 lumens.

 

[ledmax]

i direct drive a xml t6 on a 26650, its insain bright and draw 3.4 [email protected] and [email protected], used for 2month and led is still ok after 22 charg, its close to 1000lm fully charg

 

[dxcom]

Fun times, reflowed a U2 2S bin onto my MCPCB epoxied to my heatsink, attached a Ahorton aspheric lens, and got 29000 CP (lux @ 1 m) peak beam intensity vs the 23500 CP peak beam intensity the T6 was getting. A 23% increase in lux output is much more then expected, even though I was doing my best to keep the testing identical. Same lense/mcpcb/heatsink/lux meter/both measured at 5m distance, and I was getting the peak beam intensity from the same area of the projected die image. (Around the bond wires) I'll re-flow the T6 back on when I get a chance, maybe cutter didnt have the central heat pad fully soldered or something like that. (They put the T6 down originally, not me)

I was using a LX1330B light meter. the person on amazon was trying to sell it as an Extech instrument, but there is no Extech branding on it, or no listing of a light meter on Extech's website. I dont know how this meter compares to others, but regardless of that, the comparsion between the 2 LEDs should be valid.

Now for the real trick, do you trust DX enough to actually be shipping U2 LEDs? I may be a bit cynical, but I wouldnt.

EDIT: redid the T6 lux measurement, got 24750 CP for the T6, making 29000CP for the U2 only a 17% increase. The T6 is a 1A tint bin, vs a 2S tint bin, making the U2~5700k and the T6 ~6500K in color temp, which probably explains the difference between 14% theoretical vs 17% empirical. (Sensitivity of the lux meter more meant for incan/warm whites vs cool white)

So yes, they are brighter, is it noticable by eye? Maybe maybe not, depends on the on the light it goes into. Would it hurt anything getting the brighter bin if it was in a tint you like? Probably not, I wouldnt pay more then 14% extra for the theoretical 14% extra performance.

Hey CKOD,

Yes, we are actually shipping XM-L2s! Only a few lights feature this LED at the moment but we are planning to add a lot more. Will have a listing in MarketPlace soon.

~joseph DX