Nice pictures in that thread over at Shoudian. The XML apparently has three bond wires and looks just like a supersized XPG (not surprising).
The XML seems to hold its own against the SST-50. It is a bit less bright at half the drive current, but that is to be expected. Can't read chinese so I don't know if the same optics were used in the comparison. Also, a comparison using the same drive current would be better.
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SSC P7: XML has more output, a tad less heat, cheaper, no cloverleaf and more intense hotspot
Cree MC-E: XML has more output, produces a tad less heat, cheaper, no cloverleaf and more intense hotspot
SST-50: XML puts out more light at same current, lower maximum current, less heat, much cheaper, more intense hotspot
SST-90: XML puts out same amount of light at 3A but more at lower current, has lower maximum current, less heat, much much cheaper, much more intense hotspot
Heat issues is very similar to MCE/P7, though it should be a bit more tolerant of high currents (due to lower thermal resistance).
The XM-L is basically two XP-G's melded into one big LED and its cost is about 1/3 that of a SST-50.
Luminus offerings can take more power so at maximum current they put out more light, that isn't a good comparison though.
SST-90: XML puts out same amount of light at 3A but more at lower current,
I don't think that's true.
In any case, the way to compare is just look at the current (which is essentially power in this case given the very simlar Vf's) to flux graphs for the emitters. The general slope of the graph is the bin number, eg Q3, R5. The way to think about comparing these emitters is to normalize them to an approximate bin standard (let's say cree xp-g's), with a max current/power rating.
For example, a R2 xp-g is about a R4 xr-e at 1A (~300lumens), but goes up to 1.5A instead instead of 1A max. A sst-90 medium bin (WM) is in this range but goes all the way up to 9A. Similar for K bin MC-E. The xm-l has better efficacy at this lower power, like S5 on the xp-g scale (about 50% better than bins discussed, about double of a q3 xr-e, and goes up to 3A).
If you want to consider power instead (I used current to normalize since most good drivers regulate on current), a xp-g/xp-e/xml is going to be slightly cooler due to lower Vf.
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To summarize, the xm-l's are somewhat better than even top bins of quad die emitter without the gap. It's basically a significantly more efficient SST-50 that costs less.
Also available mounted on 16mm PCB board: http://www.lck-led.com/p853/Cree-XLamp-XM-L-Cool-White-LEDs-w/16mm-Board-T6-Group,1000Lm@3A/product_info.html
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