Is this a “real-world’ 20% increase in light output with an optimized reflector and driver? Or will it be realistically more or less?
For example, with the correct driver, let’s say a Fancy Fandy hoo-fire ke-hd-2010-5-897 now puts out 875 lumens with a T6. With an optimized driver and reflector, the comparable light with an xm-l2 will now put out 1050 lumens?
Lower Vf will definitely help the regulation in multi cell lights those can work with a single 18650, like Thrunite TN10-12
Whoops, misread your post. Sorry about that. 
Some german guy made some calculations.. vF actually got higher by about 46-76mV.
Basically vF decreases while temperature increases. As vF is now also rated at 85°C, its higher.
Where do you see lower Vf?
Maybe I’m wrong, but when I calculate with the old xm-l’s “temperature coefficient of voltage” which is –2.1mV/°C , I get 3.224V Vf at 3A and 85°C.
3.35V + (–2.1mV/°C * 60°C)= 3.224V
this value for the new xm-l2 is 3.35V
And because of the lower “temperature coefficient of voltage” of the new xm-l2, which is –1.6mV/°C, higher core temp means automatically higher Vf.
xml 2.0 is out? At this rate I’ll wait for 4.0 by then the Chinese Lumens will be correct on all flashlights.
Yeah, I think it’s something like that.
Although I believe that lumen ratings are weighted according to the human eyes’ response to the wavelength/power spectrum of the source, so taking into account that these LEDs are white they should really be compared to the theoretical maximum for white light (around 250lm/w) instead of the theoretical maximum for monochromatic 555nm green (683lm/w), which gives a value of about 40% luminous efficacy, meaning nearly 10% less heat.
Anyway, I wanted to put a positive spin on it 
To be honest I don’t think the increase in heat from a linear driver will be more than that amount anyway. It’s only a small drop in vf, so it should about balance out heat wise.
Wow yes, that sucks.
“Up to 20” is what Cree says. I believe I saw someone say the 20 takes into account the variability in bins where you could have one LED at the bottom of the bin and another in the same bin, but at the top of its range. That gives you 7, but that’s true of any two LED’s in the same bin. On CPF, Selfbuilt compared Foursevens XP-G lights against the newer XP-G2 lights where 20 is also thrown out and he said he wasn’t getting that much.
http://www.candlepowerforums.com/vb/showthread.php?344978
The Cree datasheet for the XM-L2 goes up to a U2 bin, but I don’t know if that will really be available. Because the LED’s are binned differently, what do you compare against? The two top bins: XM-L U3 vs. XM-L2 U2? Right now it seems like T6 and U2 are the most available XM-L bins. Once we know real-world bins for the XM-L2 and people start taking measurements, it will be easier to do comparisons.
actually, it looks like the whole top side is two solder pads, which is AWESOME
I will now have to upgrade a good many of my lights. At least I don't plan on buying any more in the near future. 
Now overdrive and de-dome it.
Neat… now to wait 2 months while someone gets them in stock
[quote=brted]
Yes it will!
Price will be nice as well. XM-L2 U2 is basically XM-L U4, one word - WOW!
I see Mouser has some in stock neutral white 5000k 75 cri T6 bin for 6.82
So, these can be ordered today from DigiKey or Mouser. Voltage is the same, mounting is the same, size is the same... Hhhmm - so, just order them and try mounting on a star? Not sure if the DigiKey U2 one can be equated to 1A/1B/1C, etc. Can that be determined from the CREE part # or that now obsolete for XM-L2's?
Am I wrong here, is there something I'm missing? Not sure if anyone said the mounting dims are the same. From the diagram above, looks like the pads are the same layout, not sure of the dimensions...
Update: Crap, not in stock anywhere. Mouser has a min order of 151 or 250, something like that. Looks like DigiKey min order is 250 looks like -- that sucks...
the T6 is minimum order of 1 at Mouser http://www.mouser.com/Search/ProductDetail.aspx?R=XMLBWT-02-0000-000LT60E3virtualkey57280000virtualkey941-XMLBWT020LT60E3
Yep, been trying thru DigiKey - found a part# for T6's of Qty 1, but now it shows no stock for Qty 1 but has stock for Qty 250 -- the game is fixed!!
Mouser has 193 of the t6 , 475 t2 and 250 t5
Yes! I see that now. So, basically you can get an XM-L2 T6 rated at the same brightness as an XML U3. Not sure how good this is, but looks like the T6 is a neutral color. Hhhmm. Are you ordering any? Anyone else? Will these really work on a stock XML star? I know the voltage is good, I think the LED (itself) size is good, not sure of the mounting dimensions.