Which setup is going to be more efficient with longer run times?

Assuming the following:
-Single 18650 cell
-Max lumen output requirement ~1000
-Typical run mode/s around 200 & 500 lumen output
-Efficiency/Run-times > CRI/Tint


- 3P XP-L2 with a linear style driver such as LD-x4

- 1S XHP50.2/70.2 with a boost driver such as H1-A

- Alternative options are welcome!

P.S Is there some type of resource where I can find the data to calculate and answer this type of query myself?

Caving lamp?

Headlamp for trail running/hiking primarily. I’d like to be able to pull an all nighter whilst carrying minimal spare batteries and ideally require no battery changes (with a 2P 18650 pack).

How important is steady output?

FET +6+1AMC works well in 500 ish lumen range

If you want max runtime from 1x18650 you aren’t going to beat a Zebralight. Since you don’t care about CRI/tint you’ll want one of the cool white models. I think the H600F Mk4 would work best for you.

what about looking for a 21700 headlight?

Can you please elaborate on that for me please?

Thank you, I’ll do some research into that suggestion.

Yes Zebralight is great and would do a good job, however part of the reason why I want to make my own design is because I want to create a smaller design for the forehead and also have the versatility of my own battery pack options e.g single 18650 on the back of headstrap (better weight distribution to Zebra), 2+ parallel in backpack/waist strap or even 21700’s etc. Not to mention I love projects like this and being able to show off my own design :smiley:

Same as per my previous comment. Plus a 21700 like the Acebeam H30 is too front heavy and would be a PITA running for hours having to constantly readjust it.

Most lights come on at a certain brightness and slowly fade, like the Streamlight Siege X USB for example:
!https://4.bp.blogspot.com/-Hd4y4lKuDxM/XMde-la1E6I/AAAAAAAAByA/KMDxKEi02fMzu7r64LzqlEFUtLLJWsKXgCKgBGAs/s1600/StreamlightSiegeXUSBRuntime.png !:Streamlight Siege X USB
Others, most Zebralights included, have more advanced internals and will maintain output as the cell drains, though they sometimes still have step downs to avoid overheating. Here’s what the output of the Tiara C1 Pro looks like:

You can see the turbo mode is still regulated for heat, but the others stay perfectly level until the light dies.

Not sure about which is more efficient but i don’t think there’s any significant difference at the output you’re planning, especially when taking tolerances into account.
Another option for a cool white tint is the 3v version of the XHP50.2 which you can then use with the LD-x4 driver.

XHP 70.2 with a boost driver is hard to beat but optics choices are limited.
Buck driven triple or quad LH351D would be extremely efficient as well. And yes, buck is needed. Even with relatively high voltage emitters like LH351D we’re talking about linear driver eating a quarter of power at lower modes.
ADDED: Buck driven XHP50.2 would also work well.

for long run time, linear driver is poor choice, the more current, the lower efficiency.

so i would choose option 2, with xhp70.2
but at 500/100 lumen, the color of xhp70.2 is not very comfortable

still at ultra low modes Buck or Boost drivers are less efficient than linear ones so if you look at runtimes

at about 1 lumen with a MCU that can simply turn off while an output pin with resistor stays switched on this linear setup wins by far as no MCU and Boost circuit eats current

also if LEDS finally hit like 2.9V at rated current Lithium Iron batteries might come into play

The OP didn’t ask about 1 lm but 200-1000 lm range.
XHP50.2 should be just under 2.9V at 1100 LED lm or 1000 OTF lm. Considering circuit losses that’s marginally too high but close enough that maybe it would work for the OP if they are just a little short of the target. But are LiFePo4 better?

@bmengineer - Right I’m following you now, I would much rather the constant current output regulation for consistent brightness.

You’re probably right and the differences may not be worth fussing about, but it’s still something I think I’d like to test. If I was to go with 3V LEDs, I’d probably stick with the more efficient XP-L2’s plus there seems to be more CCT & Bin options.

Since making the post I have realised exactly this optic limitation for the XHP70.2. I think I’d have to stick with XHP50.2 or equivalent size - the 20mm x 10mm optics are probably the largest I’d want to use.

I don’t think Buck Driver is an option because I only want single lithium cell input (or parallel) so ~3-4V.

A light with 3 leds is not more efficient than a light with 1 led, ime the opposite is true

the reason is that the 3 led light has a larger hotspot

so, efficiency favors a small hotspot (deep reflector)
efficiency favors Low CRI
Low CRI has more green, and less red output… green is a more efficient color for our vision

efficiency favors low lumen levels

sustained high lumen levels, require high battery capacity
sustained low lumens (less than 200), favors lower battery capacity

example, the sustained lumen capability of a single 18650 light is about 300 lumens constant

It was my understanding that that for example 1x XP-L2 (V5) @ 1000mA = ~451lm and 3x =497lm. For the same given power, is this not ~10% more output therefore more efficient?

So if I understand you correctly, what you’re saying is that the extra lumen from a triple LED isn’t necessarily noticeable? If anything, it detracts from the perceived brightness?!

lumens is all the light

a triple puts all the light, onto a larger hotspot than a single
assuming the triple and the single are set to the same lumens total,

the triple will look dimmer because the light is diluted over a larger area

hotspot size example, triple on left, single on right

iow, a single will throw farther
a triple will be floodyer

theres a time and place for both
the triple at closer range for wider illumination
the single to reach out farther to spot a smaller target with less close range sidelight glare

OK I’m with you now. Wouldn’t the optics have a significant contribution to this also?

It just so happens that I need a floodier, wider, closer proximity beam for illuminating trails at night so I think a triple will still suit my needs.

There are buck drivers designed for 1s Li-ion input.

Good point, it’s about whether the OP want lm/W (total output) or cd/W (total intensity) or something between.
Fewer emitters (as well as smaller emitters) favour the latter, more favour the former.

Most earlier answers (mine included) offered exactly what the OP asked for - lm/W. But quite often this is not the right metric. Or rather - it’s not the only one that matters.

Also, as long as the throwiness gauge is on the right or in the middle or a little to the left, flat emitters are more efficient

So…a large flat die is the most efficient general-purpose option.