as a former Ultra-light backpacker, i know that Photon Microlights are all the rage w/this group of "gram-weenies" as we affectionately refer to ourselves.
however, ANY microlight operated off of Li coin cells is a very inferior illumination source. in fact, i'll go as far to say that ANY light (i probably own virtually ALL of them) operated off of Li coin cells (even FOUR such cells in a parallel-series arrangement) is an inferior illumination source, IMO (YMMV).
every light output curve that i've seen, whether a single mode light, or a multi-mode light (e.g. Petzl e+LITE and PrincetonTec Scout) operated on HIGH, after only 15minutes of continuous operation (30 minutes at the most in any Li coin cell powered light) is outputting only 25% of its initial light output. for example the ~300 lux of the e+LITE on HIGH (3x5mm white LEDs) is down to ~75lux somewhere b/t 15 and 30 minutes (my "old-timers" is actin' up and i'm forgettin' the exact time, though i'm leanin' towards the 15min number).
far, far better for long burning, small, lightweight task/proximity lighting is a 9V Pak-Lite, an Arc-P, a Fenix E0 (no longer Mfr'd), or a Fenix E01. there really is no comparison between them and a coin cell powered microlight. once i used one, this "weenie" was more than happy to carry a bunch of extra "grams" to have a superior source of task/proximity illumination.
the best thing that i've done with some of my many Photon Microlights is to sacrifice the clip mount that comes with it, modify it slightly by clipping off anything that protrudes upward from the flat base, use some sticky back Velcro that comes with the 9V Pak-Lite and use the hook Velcro on the now flat surface of the Microlight clip mount base, and loop Velcro on a light's body even if it's round/cylindrical (or rechargeable 9V battery for the Pak-Lite) to make a very nice directable hat brim, pack-strap clip for these other small lights to permit hands-free operation.
give it a whirl and i think that you will become a convert to the anti-microlight faith too.
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my favorite small 1xAAA light right now is the LiteFlux LF2XT. it is so flexible in terms of its user configuration/"programming" that it would be the one light i would definitely take if i were going "ultra-light". the fact that i can configure it for VERY-low output levels, yet also for brighter output (albeit with a much shorter burntime) makes it a "must have" don't leave home without it for me (either on an evening stroll in the woods or to the office for work). it is an EDC for me now. i have two of them. on one of them, i've left the standard included clip on the light. on the other, i removed the clip and installed the included "ring". the ring plus a plastic quick disconnect from Lighthound.com allows it to be securely carried on a key-ring or "biner" in the pocket, yet quickly removed using just one hand for use. i've also added a Fenix AAA-body clip to this second LF2XT to allow bezel up carry in the pocket, but really more for clipping the light to a ballcap or visor brim for hands-free operation.