Okay, stop getting hung up on printed spex.
If you look at, say, the Jetbeam Jet-I, you’ll see 2 different lumen ratings, one for Li, another for alkie. When you take multiple chemistries (and voltages) into account, you’ll get different performance.
They (being a reputable mfr) won’t just list the higher lumen output for Li cells, because then anyone using alkies will go bitching’n’moaning about not getting near that output when using alkies or Ni-* cells. And that’s when you’re feeding the light with up to 4.2V vs 1.2V!
Runtime when using moonlight mode, I can guarantee you, won’t be specced out for each’n’every chemistry when you’re using alkies, NiCd, NiMH, etc. Most people would care about light output at its maximum setting, not runtime using the lowest possible setting. That’s pretty much an afterthought.
But again (and again, and again, after multiple people suggested the saaaaaaame thing), TRY an AA alkie, and see how that fares.
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Want a better example?
Buy a car that costs big bux, one that runs off E85 (“flex-fuel”, etc.). EtOH does not have the same energy density as straight gasoline, so your gas mileage will be lower using E85. Hell, my car’s mileage drops some with “oxygenated” fuel in winter.
Do you complain to Ford, GM, Toyota, etc., for not including specific fuel-mileage spex for straight gasoline, 10% EtOH in winter, E85, and so on?
You’ll never see those spex, because it’s presumed your mileage will drop with different fuels!
Yet you want to hold the maker of a 15buk flashlight to even higher standards? C’mon…