Fenix HM 70R
About 18 months ago I wanted a new headtorch, and thought that the Fenix HM 70R seemed to have a good specification, though I was a bit put off by the fact that it takes a large battery – a 21700 / 5000-mAh thing, as opposed to the more common 18650. I then noticed that Fenix sell an 'adaptor' which is just a short tube with a spring inside that enables you to use the smaller battery in the 70R. So I bought one.
The lamp has three modes – a flood-light setting, a beam setting and a red light. I'm not a big fan of flood-lights, and much prefer a beam, as long as it's not too narrow, and the beam on this lamp has 4 settings – 30 / 150 / 500 / and 1600 lumens, with a claimed run-time of 100 / 30 / 6 / and 2 hours, respectively.
I find that the beam on the 70R suits me; it projects a circle of light roughly 38 cm in diameter at a distance of 1 m, with a dimmer circle about 135 cm in diameter surrounding it (though as the light circles are not hard-edged, these figures are only approximate).
In use underground, I would say that the lowest setting (30 Lm) is not much good. I checked out the performance of setting 2 (150 Lm) in Mistral, which has a combination of small crawly passages at the entrance, bigger walking-sized tubes a bit further in and larger passages with light-absorbing mud-banks deeper in the cave. Setting 2 was fine in the crawls and walking-sized phreatic tubes, and adequate in the bigger passages, while setting 3 (500 Lm) is obviously much better; in my opinion the latter provides a good bright light.
As regards run-time, I tested both settings 2 and 3 but didn't bother with 1 and 4. On setting 2 it gave something like 17 hours light with a little diminution (but not much), after which it started to get dimmer, but it was still giving a 'usable' light after another 3 hours, at which point I got bored and discontinued the test.
On setting 3 it gave 5 hours of light with a little diminution (but not much), and at about 5¼ hours the light output dropped off noticeably. I let it run for a bit longer, and after another hour or so it was still giving what would probably be a 'usable' light underground. I also tested setting 3 with a 18650 battery (3500-mAh), and it gave 3 hours of good bright light; by inference, it would presumably be good for about 12 hours on setting 2.
So – in my opinion this headtorch gives ~5 hours of good bright light, or 17 hours of 'adequate' light on a beam that's not too 'spotty', with a bit in reserve on both settings.
