180 hrs at 20 lumens, 120 hours at 100 lumens according to the REI page (replaced by new model 60 hrs at 200 lumens, 240 hours at 5 lumen red I believe)
Just as a FYI, no set of 3 AAA batteries will deliver enough energy to light a LED at 100 lumens for 120 hours or 200 lumens for 60 hrs.
According to Petzl, The measurement is made from when the lamp is turned on until the user cannot move for lack of visibility; this value has been estimated to be 0.25 lux at 2 meters (equivalent to a full moon night).
I did not find any data on what batteries are used, but based on the curve shown on the website it is likely alkaline batteries. Nimh or lithium primary batteries will provide a more constant light output, but will drop off more quickly at the end, especially the lithium primary.
Sorry if this is excessive thread drift but the realization of the sort of advertising quoted above is what turned me off from mainstream headlamps. Of the bunch the Petzl e+lite is still a decent lightweight alternative that provide pretty good output for a long time, due to using two lithium button cells.