I calculate approximately 160 lumens/watt over the entire regulated run-time, with my Zebralight SC600w MkIV Plus. It might be a bit better, since I can't get the last bit of juice from the battery on a regulated output. I think it's supposed to be one of the most efficient lights available, and uses a Cree XHP50.2 emitter. Though their SC700d might beat it, using the XHP70.2.