I’ve recently become interested in ultralight backpacking. I’ll purchase some BLF lanterns for sure, but they also aren’t ultralight for sure.
The useage is: 4 person group hike and camp over the course of 5 days/60miles, all at 9,000+ft elevation including two 14k peaks, and no resupply stops (i.e. carry all gear including 5 days food) so every gram counts. Use 2 (maybe 3, but testing appears that 2 is plenty) camp lights of ~150Lm each to light the small 20’x20’ campsite at night for drinking and storytelling (each hiker will have a personal headlamp).
Here’s my proof-of-concept (I shouldn’t even call it a prototype):
- High capacity 18650 (magnetic leads)
- Adjustable DC step-up voltage regulator set to 5.200v at the moment
- XHP70 (will be xhp70.2) in 6V mode
Based on great feedback I got here on BLF (thanks kiriba-ru, others!), I used an XHP70 emitter I had available due to the extreme efficiency multi-die emitters can acheive at low currents. This setup measured 137Lm at 5.201v/0.060A across the LED for example. When I make the finished product I will use an XHP70.2 to hopefully get a tiny bit more efficiency. The output above equated to 0.090A from a 3.9v battery (88.9% efficiency from the step-up regulator, not bad!) and 0.12A from my power supply set to 2.9v (89.7%). Based on those number I’d be looking at 30+ hours of runtime, ignoring temperature influence (see below).
I only had a 12v MCPCB on hand, so I soldered lead wires straight to the LED. At 0.06A there was no heat to worry about for testing, although the final product will be properly reflowed on an MCPCB.
Right now I’m playing with optics to decide between mule mode or using some optic. I’d love to find an elliptical optic for XHP70 footprint, but so far haven’t found anything.
I tried to use dedicated 5v step-up boards, but the LED output at 5v was too low, about 25Lm.
Currently the setup weighs 53.5g (the battery is 45g) without an MCPCB (2.5g).
Nighttime low temps could be as low as 20F, so I am considering replacing the 18650 Li-Ion with 3*AA Energizer Ultimate Lithium primaries because the Lithium primaries should perform much better at low temperature. The Li-Ion will probably lose a lot of capacity in temps that low and I don’t want to bring extra cells. There is no weight penalty as AA Lithium primaries weigh ~15g each.
I need to determine a good method to mount the lights for use, either hanging, or staked in the ground, or … still brainstorming that part.
The final product would have SOME simple protection for the LED, the PCB protected with some conformal coating plus electrical tape, and the hole thing will be generally cleaner looking, but overall not fundamentally much different than pictured.
Thoughts and feedback are encouraged!