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So the brightest CREE XHP35 LED (5700K Low CRI) produces 706 lumen at 350mA (25 degree celcius). At it's absolute max current rating of 1050mA it produces 2.4x it's rated lumens. About 1700 Lumens. At a realistic temperature of 85C it can produce about 1,500 lumens. 1,400 with a middle ground BIN LED. Impressive but it will never reach 2,000 lumens unless they are driving it well past spec, and even then only for a second.
All XHP35 LEDs are "High intensity", it's just part of the description, I've been looking at the correct data sheet this entire time...
So by eyeballing the flux/current graphs (speculating a trend past 1050mA) they would have to be running over 1300mA for a reading of 2000 lumens. Roughly 25% over maximum current rating assuming they are actually using the group with the highest output. Even if the temp on the review was die temp and not exterior temp that could only account for 8-10% of the output over the 1500lumen 85C spec. I'd be interested to see what current they are actually pushing through the die, but I don't see any way they could be doing it without pushing the LED well out of spec. Now that I think about it I did that with the 25C lumens when I should have done it with the 85C lumens then added a bias for the estimated die temp, which would likely make the estimated current go up.
Also, zeroair is a very trust worthy reviewer. So if he is saying 1984, which is near enough it makes no difference. I believe it.