It's worth looking at the Nitecore range. I have a PD10 which takes a single AA, which I'm pleased with. The brightness is continuously variable from around 2 lumens up to around 130, with runtimes of 55 hours or 1 hour respectively. It has a piston switch which can be used as a twisty, a clicky or momentary on. It runs on any kind of AA, including rechargeable, lithium, and plain old alkaline. I normally use Eneloop low-self-discharge, and that's what I used for the runtimes I cited.

It's small enough for every day carry, which I do. They also have a 2 AA version which is bigger, and rated at 180 lumens, but I've not tried it myself. The build quality is good, apart from an early batch. It's water-proof.

It's not perfect. Some people can hear a whine from the step-up circuitry; I can hear it on mine if I hold it close to my ear on full brightness, but I can't hear it normally. Younger people may find it worse. I don't think it's an issue with 2 AA because that's starting from a higher voltage. In any case, it's not really a tactical light - no strobes or whatever. The UI is pretty simple if you use it as a single-level light, but could be improved. (I'd rather it had 5 or 6 discrete levels instead of being continuously variable, for example.) The lanyard it comes with is a bit bulky - I took the clip off it and attached it to a lanyard I made myself from paracord inner thread, which I keep in my wallet.

Overall it's a very good light. I'd considered the Fenix lights and rejected them because their dimmest setting isn't very dim. The Nitecore's dim is just enough for reading in bed, or for navigating the house with dark-adapted eyes. The Fenix has a more efficient driver, but because it can't go so low its maximum battery life is shorter. I'd rather have dim, partly because it's useful in its own right and partly because in extremis I want the long battery life. I want bright as well, of course - 130 lumens is brighter than the very expensive, and physically large 2x132 Surefire U2 I bought a couple of years ago.

Running on a single AA is great, too. An hour on bright with rechargeable makes it practical and economical for walking the dog etc. 55 hours on dim makes it a good emergency light if you get trapped in a cave. Lithiums are expensive but have better performance, especially in the cold. I've taken to caching single lithiums in odd places because they are relatively small. And of course you can raid other equipment for alkalines if you have to.

I think this shows how technology has improved in the last two years.

I bought from 4sevens.