Caving Headlamp – Overview
By Ian Mander 5, 7-8 November 2010.
After much pondering I've come up with a reasonably detailed caving headlamp design that should be rugged enough and waterproof enough to survive just about anything that is likely to come up in a caving trip. It combines the efficiency of the latest LED technology with enough maximum output to illuminate the largest of cave chambers, and provides very good runtimes from 4xAA Eneloops at normal illumination levels. Total cost will come in at around NZ$105.
The headlamp and battery housings are both IP65 rated aluminium enclosures. The cable between the two is rugged enough to cope with caving abuse, and conductive enough to have minimal voltage drop even on the highest mode.
The headlamp has four Cree XP-G LEDs, individually driven but switched in two banks. The two banks have different wide beam and narrow beam optics. Each LED bank can be operated independently of the other, in any of five modes. This effectively gives 25 total modes with each having a different lighting pattern. There is no switchable off setting but the battery pack can be disconnected manually inside the battery housing.
4xAA Eneloop cells providing power for 156 lumens for 8 hours seems quite extraordinary; this is close to the peak system efficiency.
Stepping down a couple of modes, with a system efficiency almost as high is 85 lumens for 14 hours, using one LED on idle and one on medium - 85 lumens should be plenty for ordinary caving. (Compare that with my last single LED headlamp, which provides 75 lumens for 6 hours on 3xAA Eneloops.) Remember, there are two combinations providing this level of light, so the beam pattern most appropriate for the situation can be selected.
Turbo for either bank can be selected at any time, but both are momentary to discourage overuse of the mode, since it really does chew up the runtime. Because it is a separately selected momentary mode, turbo is not selected when clicking through the standard modes. Turbo should light up cave chambers like no other headlamp available.
The other pages provide some details and thought processes into component and setting selection.