I've had a P1d on my belt for about 5 years at work and otherwise.
Alot of times I am carrying a bigger primary light, but the Fenix P1D CE is always there, Tiny small, almost weightless, Very bright in a small package. It comes with a Belt Sheath.
I used it alot at night to take closeup pics of locks and alarms and operate it with one hand although it is a multimode twisty.
I've dropped it drowned it etc and it;s still as good as the day I purchased it.
No matter what other lights I'm using I always have this backup and in some cases use the smaller one over the others for various reasons.
The Batt lasts a fairly long time the way I used it, usually at least 2 weeks. It's a CR123 and you can get rechargables for this if you want The regular batts are cheap if you buy them online do a search on CPF here.
This light, if your not familiar with it is about the size of your thumb, slightly longer than the CR123 Batt. that powers it.
For an always there, never a burdon, light as a feather, and brighter than most average 3D cell light torch, I say go small or even to the same form facter in a 2 CR!@# light such as a P3D (not sure of the exact name but some guy is selling one on a thread somewhere here NIB for 50 Bucks that is 215 lumens and a bit longer than my P1D.
I answered what I assume was your question, not for the best duty light, but for the best belt backup light to always have handy when your main light loop is empty.
try looking at the fenix tk10. Great light IMHO, Build is very strong, Very Bright on high and price is a lot lower than when I purchased mine. High and low only and runs off 123a's. Still a go to light.
Welcome to CPF!
Chef
I use the TK 10 or Mag85 in my belt loop as Primaries, and your right its a great choice, I use it every night and it's surprisingly weightless feeling (the TK 10 ) to carry in a mag loop and both have stunning brightness for what I do. I don't always want to lug a light around so sometimes the TK 10 and Mag85 stay in my P.V. It is then that I appreciate the never thought of but always there when I use it every 5 minutes P1D.
EDIT: BTW I don't think Fenix makes those anymore (the P1D) but they make something very similar, just called something else and not as pretty. They still make the P3d's tho I believe. These are small, handy, light, reliable twisties that take up little belt room and weigh nothing. For tactical lights you would probably prefer something else. Fenix and many others sell lights more suited for tactical use, but I think your looking for a backup or casual light to have on your belt when you don't have your Stream or Stinger with ya.