The debate is still going on about who makes the best single AAA battery flashlight for lightweight backpackers - Arc or Fenix? Fenix has a new version of their L0D available August 20, the Fenix L0D RB80 which uses the Luxeon Rebel LED. Circuitry is unchanged and run time is about the same as the previous version but it has more output - 60 lumens in the bright mode as opposed to 50 lumens for the Cree 7090 XR-E LED.
Although the Fenix L0D and Arc-AAA lights have similarities: same size, AAA batteries, and housed in aircraft grade aluminum cases, they are quite different in function. The Arc-AAA light is meant to always be there when you need it. It has only one - low - mode of 5.5 lumens with a run time of 5 hours to 50% brightness and still outputting diminished light after 12 hours. The light is switched on by twisting the head, which can be done without unclipping the light from your ball cap.
The Fenix L0D adjusts from medium to low to bright to strobe to SOS by twisting the head on and off repeatedly. It has much brighter options than the Arc-AAA. One complaint is that switching requires two hands and is hard or impossible to do with the light clipped to a hat.
Both lights operate effectively with Lithium batteries.
The L0D RB80 is bright. On bright and aimed at my eyes from a few feet away, it made me squint even in daylight.
This new Fenix light will probably not convert an Arc lover over to the Fenix side, but it'll make users who want a very bright light in a small flashlight with easily available batteries happy.