Originally Posted by Cyclaholic
According to the specs they're Q4 bin. If they're being driven at their rated 3 watts and the heatsinking keeps the junction temp down to 25deg.C then the LEDs are good for about 880 lumens total. I would allow about 5% loss through the optics, so about 840 lumens effective output.
Actual out the front lumens are typically 30% to 35% less than emitter lumens, due to reflector losses and the front "lens" losses. That would give more like 580 lumens out the front. Of course, its hard to compare with other lights because manufacturers tend to spout emitter lumens and not lumens out the front of the light.
The other thing is that the Romisen does not drive these four Cree LEDs at 700 mA (or close to 3 watts as you say). They are actually driven at about half that, so cut the 580 lumens number down about 40% to 350 lumens.
Still, its a pretty good value for a 4 Cree light if you can get one (they seem to be out of stock now).