Super efficient build

Hi guys;)
I’m going to build a new light. My goal is to get best possible runtime in range of 600 - 700 lumens. Which led or probaly leds gives me best lumens / amps ratio? Maybe 4 x XP - L ?
Also … Im looking for host. New convoy s11 look pretty sweet, isn’t it? Which compatible optics would be best for tighter spot?
Best regards;)

Max regulated runtime, or max runtime ’til it crokes?

Former, get low-Vf LEDs (most headroom vs cell voltage).

Latter, just go for the most efficient LEDs.

But yeah, maybe XP-L2s.

Keep in mind, though, that even going from right-out-of-the-charger, to warning-blinks-then-dead, the difference in runtime won’t be that significant. Guessing only 10% or so, for most 1-cell, 1-LED setups.

You’ll buy only a hair more efficiency with 3-up and 4-up lights. 4-ups might even be less efficient with smaller lenses (ie, more optical losses) vs 3-ups. And some lights with 3-ups lose more light because of a bezel that partially obscures part of the TIRs!

Don’t stress the light, and just slap in some 3400mAH-or-better cells.

So… I wouldn’t fret about wringing the last percentage of “efficiency” out of it.


My guess is XP-L2 V6 in the Wuben TO50R would be one of the most if not the most efficient flashlight you will get.

The best way to get maximum efficiency from ANY LED is to use less current. The way to use less current and still get enough lumens, is to use more emitters. So, to get 600lm output, go for 3x 200lm for better efficiency. Or even 6x 100lm for monstrous efficiency!

Here’s an example from CREE PCT data, using the aforementioned XP-L2 V6 emitter:

1x - 604 lumens using 3.5W of energy

3x - 601.5 lumens using 2.97W of energy


A buck driver, with 3x XP-L2s, and bypassed springs would be your best bet for absolute best efficiency.

Well, there’s also the led4power 6x board and Ledil Anna optic, which would make it all the more efficient. And according to djozz test, the SST-40 beats the XP-L in efficiency. Even though the XP-L2 is much better than the XP-L, a comparison with CREE PCT data looks to still favor the SST-40 by a little. But, sadly, led4power doesn’t make his 6x board in 5050 footprint, only 3535 or 4040. So, I guess it’s back to XP-L2 if the 6x board is to be used.

If you want maximum efficiency something crazy like a 3V XHP50.2 quad would be the best but very floody, however if you want a tighter beam you will need to compromise and use less LEDs with more throw.

Something like the Sofirn C8G with the XHP35 HI would likely be a good compromise between throw and efficiency if their boost driver is efficient enough, but it’s UI is far from being BLF’s favourite.

But you can build 6x Luxeon V (you can mix. 4000K and 5700K to get any CCT in 4000K-5700K range), those have ~190lm/W at <350mA, and probably ~200lm/W at ~200mA, which should be enough for desired output. Tint is much better than XP-L2 too.

EDIT: Upper lm/W are based on Maukka measurements, but those are done with (long gone) first batch of Luxeon V which had higher Vf bin than newer Luxeon V, so efficiency should be over 200lm/W@200mA.

How about putting a Skilhunt H03 buck driver into a Emisar D4? :smiling_imp:

The way luminous efficacy/efficiency is defined goes against light quality. Use a nice green emitter for maximum efficiency. Just to let you know. ;-)

Flashlight with good fully regulated drivers (buck, boost) provide somewhat better efficiency.


All this is why I want a Luxeon V in my Zebralight. Alas...

But yeah, you need to start with an efficient driver (which we don't have great options for around here) and finish with multiple and/or low Vf LEDs. To some, it's easy to go 6V boost driver and a 6V XHP70, since it's 4 XP-Ls (forget which type of XP-L). For me, I'd mess around with something like 3 Luxeon V in a C8F or 6 in a Ledil optic, and try to find an efficient driver... Dunno how much better than AMC7135s you'll get though

DonkeyBoy aims to build something, and he seems to be flirting with an S11 host. Kaidomain's ∅22mm H2-C driver (also available in AliExpress' LHT Flashlight Store) fits nicely, being an efficient fully regulated boost driver intended for XHP35 (4S) emitters, which can be easily modified to drive 2S emitters. For detailed information check this thread: Buck and Boost Drivers, Testing, Modding, and Discussion (Pic Heavy). The details for H2-C modding are in Jensen567's Entry for the 5th Annual Old Lumens Scratch Build Contest - Machine Made Category, but I doubt the driver strictly requires output voltage divider modification to drive 2S emitters when driven by 1S battery input. I mean, I think it should straight work with XHP50/XHP70 emitters.

In any case, an XHP35 build will hardly be less efficient. On the other hand, with an XHP35 the flashlight will be throwier. And with an XHP35 HI, a lot throwier.

For big throw, I'd go with this host:

Note: use BLF coupon to attain 5% discount at Kaidomain.

Give thanks if you like. O:)


Thu, 06/20/2019 - 19:21

With emitters that have really low forward voltage (like luxeon v), shouldn’t a buck driver be feasible with a single lithium ion cell? This should depend on dropout voltage, I suppose.

I don’t see any high current buck drivers available, but if you don’t need 1000+ lumens, there are some options…

Stepping up in size to a 21700 can significantly increase your runtime as well. 5 Ah with good enough current capability is available.

Assume 200 lm/w and 90% buck driver efficiency on average, with this setup you have 5.4 hrs of 600 lumens.

Efficiency wise:

That is an H2-C driving a 2S emitter with 1S battery input, sense resistor modified to ≈R018. Efficiency is ≈90+% and low mode is current spot on to obtain ≈700 lumens from an XHP50A. With an R020 low mode would be ≈590mA, a bit above 600 lumens and guaranteed more than 4 hours of runtime with a high capacity 21700.

All of these numbers are feasible and tested.

What's up with moonlight there, Barkuti? Is the output so low that the current draw of the driver electronics like MCU itself start to be significant compared to the LED's draw?

Thanks for lot of answers;)
First of all I have to put those parts into convoy s11 host, so 20mm mocno and 22mm driver only;(
Which suitable optic wouldy best for throw? Im not gonna build a thrower but i dont like flooders…

Scallywag if you refer to the relatively low efficiency of the lowest mode, I guess that is a yes. The average input power from 4.2 to 3V is ≈0.134W (did not include de 2.8V value in the average, albeit it'd hardly make the figure go up). Considering the close to 75% efficiency in that voltage range, this means ≈0.034W or less than 10mA of average current consumption in the driver due to MCU, MP3428 boost IC, linear regulators and other stuff. So maybe it's not the most efficient thing to run in moonlight levels, but no big deal here.

DonkeyBoy a smooth reflector usually is the best option throw wise, although it too depends on reflector shape of course.


First off, WELCOME to BLF!! :beer:

I would argue here that lux/W could be a more relevant value to focus on (sorry for the pun) in your application. I’m assuming this since you mentioned throw and have a fixed, relatively small optic you’re working with and didn’t mention a headband or tailstanding. Mind sharing how you’ll most likely use the light 80% of the time? Max distance? Direct lighting or ceiling bounce? In a brown cave or a sterile white office? Is there ambient light or complete darkness?

I’ll make a few points to support my reasoning here. First of all is the way we perceive light. In a focused beam that an average flashlight will produce, against a white wall, 2000 vs 1000 vs 500 don’t look all that different. In a ceiling bounce scenario, however, when light is diffused over a larger area and intensity is lower, changes appear more linear - especially at very low levels. Additionally, our field of view of what’s (mostly) in focus is less than a 10 degree cone (see wiki image below). So if we are outdoors in a handheld, point-it-where-you-are-looking application vs a close range fixed/diffused source like a ceiling bounced torch or headlamp, “efficiency” is very different. First case, a winner would be an XP-HI or SST20 or Osram Flat series in a large SMO relector. In the latter, a multi-emitter mule would win out.

In a typical EDC torch, I find it best to use an SMO reflector with diameter:depth ratio around 1:1 and target a 8-10 degree hotspot with a narrow carona. Since most times the optics effective diameter is between 18 and 22mm, that lands me on a domed SST20/XPG2/219 or a XP-L HI most times. In a setup like that, you have enough beam width to adequately see and focus your eyes on a target, yet don’t need to jump to turbo to see things at 15 meters distance. Also, 80CRI is a good compromise on light quality and efficacy. This again could be more or less important based on your use case.

For you, assuming you go with the Convoy S11, I would have to agree with some others here and recommend a Luxeon V as the emitter. It will pair wonderfully with the 28mm reflector and they have great beam/color quality. I’m not up-to-date in the driver world, so I’ll let others chime in on what the best choice these days are.


A recent similar thread:

What do you guys think is the most efficient AA/14500 light (or driver/emitter) out right now for low currents?

I’m looking for something that will last a very long time for ultralight backpacking, but only would need a range of 1 - 100 lumens, with the vast majority of the time around 1-10 lumens.

Is the XP-G2 the most efficient for that? I saw there’s a new higher efficiency XP-G2 model out but no one is using it.