I got a diver's light, mucho waterproofo, a little four-cell AA that I carried in my jacket or back pants pocket.
This was perfect. Not too large, had a bright beam and a lot of throw–which, as I understand the term, means it projects a focused beam a long distance. (A laser would have the most throw, whereas a lantern would have little, like a table lamp.)
It's still my jacket-pocket carry once the weather turns wet and cool.
But having been inside a large hotel once when the power failed and the emergency lighting said, Nah, I ain't working today, sorry, I wanted a small keychain light, just in case.
Yeah, yeah, iPods and iPhones and like that have a flashlight mode, but them's weak tea.
The cheapo keychain lights aren't much, so I upgraded to a AAA Fenix E01, which is about the size of my little finger. The single LED was much brighter than those throwaway squeeze jobs, and the AAA battery easy to replace.
More than a few times, I've been fumbling for something in my car, or looking for something I dropped, and this light has done the trick. Convertibles don't have a dome light, and the one over the rear view mirror is dim.
So the Fenix was rugged, dependable, a great ECD. (That acronym I came across recently, hadn't noticed before: Every Day Carry ...)
Um. Then I found out that Fenix makes a AA model, the LD 15, which is slightly larger, but since I use AA batteries for all kinds of things and have rechargeables in that size, I figured what-the-heck, so I got one.
This is larger than the AAA, of course, but not so large I can't use it on my keyring, and it is waaay brighter, plus has two modes, a dim one that will last for thirty-some hours, and a brighter one good for like an hour and a half. Not much throw, but for what I usually need, this is fine.
So that's the current EDC darkness-banisher ...