I would guess that photon puts out a lot more than 4.5 when the battery is fresh and rapidly drops to about 4.5 and rapidly drops again to even less. Unless they're semi regulated now (Mine I don't think are regulated at all), the photons have very quick drop off. The E01 is fully regulated for something like 10 hours them semi regulated for another 10. The flat-ish output is what I like so much about it.

EDIT - I should say the ARC AAA has similar performance to the E01 except about half the regulated run times, if memory serves.