Why is that?
Both a 14500 Li-Ion cell and a AA NiMH cell have about the same overall energy when delivering low current, so you would expect them to have similar runtimes if lumen output is the same. Therefore, one of the following is happening:
1. Light output on NiMH is actually lower than on Li-Ion
2. If light output truly is the same (5 lm), then the above runtimes are wrong.
3. If light output truly is the same, and the above runtimes are correct, then this driver is wasting a lot of energy when running on lower mode when using a Li-Ion cell.
Looks like a great AA headlamp. I have the Acebeam H30 and while I like the 21700, high output, and form factor, I don’t prefer the CW tint and don’t need the green/red emitters, which I’m planning to swap out in the future for Nichias or Optisolis 2000k and 5700k.
Also what tint bin is the SST-20? I hope it is not above the BBL again. I have the Acebeam EC65 219C version and I don’t like the greenish tint so I won’t use it until I swap the emitters. Otherwise it would have been a great 21700 light.
The website seems to indicate a ramping mode of 20-230 lumens, with an “ultra” low of 5 lumens and a turbo of 350/1050 lumens or 250 lumens. It also mentioned ramping controlled by a single button. So I guess no dial. 
My impression from reading spec sheets of various lights is that this is pretty common in the 1AA and 1AAA lights. The Li-Ion just don’t seem the have the low output longevity that NiMh have.
If I had to guess, actual lumen on low when running on li ion is higher than when running on nimh. I have yet to see an AA light that has the same output moon mode on both li ion and nimh.
So is there a promo code Acebeam?
I like the T-shaped from factor, 34 gram empty weight, and 1050 lumen Turbo mode, but it appears that three discrete modes are combined with some form of ramping, i.e.: "infinite dimming outputs ranging from 230lumens to 20lumens by Li-ion battery, ranging from 230lumens to 20lumens by Ni-MH or Alkaline AA battery". How is this accomplished? Another question, can Turbo Mode be accessed from Off? An in depth explanation of the UI is required before a purchase decision can be made. Perhaps Acebeam could provide an H40 to a BLFer in exchange for a review that may answer some of these questions.
What the heck? Post and left. That not cool in my book, Acebeam.
Code please… 
My hl just sits here. The flashes at the top and bottom of a ramp cycle is just too annoying for me.
Along with a lack of a moonlight or sub 5 lumen mode.
Anyway, is it possible to get Narsil in this hl?
Thanks
Grabbed one of these; nice size and form factor. Too bad it doesn’t work.
It runs for maybe 30 seconds on a NIMH then shuts off. On a 14500 it won’t power on at all.
Sounds like a dud, did you get from an “authorized” retailer. Either way contact the retailer then AceBeam or heck contact both at once let them know, don’t let them sleep.
Contact the OP via a private message,
I agree with Chooma, but otherwise the two H40s that I have work fine. Purchased them from Amazon. WhiteDragonBC, where did you purchase yours? Take care.
Nitebeam US on Amazon. Already sent it back.