Helmet mounting?
Fenix E15, 1x AA, 105 lumens, £23.95
Fenix LD12, 1x AA, 120 lumens, £44.95
Fenix PD22 S2, 1x CR123A, 200 lumens, £45.95
Fenix PD32 S2, 2x CR123A / 1x 18650, 330 lumens, £55.95
Fenix PD32 UE, 2x CR123A / 1x 18650, 740 lumens, £59.95
A few other emitter variants are available, Ive tended to go for the better ones as they're only a pound or two more expensive.
A couple of thoughts:
The E15 is plenty enough for an emergency light and for a bit of extra illumination. It's cheap and only has a couple of modes, but it's £21 less than the LD12 and isn't appreciably less powerful. It runs of a single AA, so it's no hassle to find a battery for it.
I've not seen a PD22 in the flesh, but it's going to be pretty small for the output and thus has light weight in its favour.
The PD32 S2 is a great bit of kit and gives a lot of light for the size.
The PD32 UE is brand new and I've just got my paws on a few today (the main importer is now sold out). There's a thread elsewhere on it, but a couple of initial comments: firstly, the output is phenomenal for the size.
Secondly: it's a bit bigger and a bit heavier than the 'standard' PD32 as it's got a big heat-sink on the head. My suspicion is that it is small enough to helmet mount, although you might be reminded that it's there.
The 740 lumen output, incidentally, is a 'turbo' mode only - it is heat-regulated and will step down to 400 lumens after three minutes.
More thoughts on the PD32 UE in the appropriate thread later...
Hello again darkness, my old friend...