Emitter recommendations for Fenix HP25 swap

Hi all, been lurking on and off for years but finally made an account.

I need some advice on modding a Fenix HP25. I really like this headlamp, the flood is super even and the throw is the tightest beam I’ve seen in a headlamp. One downside is the 4XAAA pack on the back but that’s not noticeable when caving with a helmet.

Unfortunately the emitters are very cool and low CRI, and also outdated with pretty poor output. Both are Cree XP-E and I’d like some recommendations on what to swap them with. They are 3v and I think the XP-E are limited to 3A so I would need emitters that do well at that current. I’d like 4000k-5000k and at least 80 CRI (more would be preferred) for the flood. They are on 17mm dia PCB.

Throw reflector has a 6mm hole in it.
I’d be willing to drill it out bigger if need be. Flood emitter has a little optic on it. I thought it was glued but it clips into little holes on the PCB. I have no preference on keeping vs ditching it. I like the flood to be even intensity from center to the edges. Any recommendations for good emitters and where to buy them on a PCB? I’m very open to using different emitters for flood and throw.

I made a Reddit post here with pictures.

Thanks for any help.

Several choices although you might lose a little throw since the XPE is a smaller emitter. It uses the common 3535 (i.e. XPL) footprint. The Samsung LH351D emitters are very nice and available in high CRI and a variety of color temps. The Luminus SST20 might be a better choice but the neutral white temps are typical 70cri I think and only the warmer >4000 are high cri. At 3 amps you shouldn’t really see much green in the tint with either of these but either would certainly be nicer than what you’re used to, high cri or not.

The newer versions of the XPE have kind of ugly color tints and color rendition, but they’re slightly more efficient and slightly brighter if you get the good bins.

Some links to the Convoy store where you can get them either bare or mounted on copper mcpcb’s. One question is the actual size and shape of the mcpcb. 17mm is a little odd but these days we see lots of unique boards specific to manufacturers or models. Simon only sells the typical mostly-round 16mm and 20mm boards. Might compare photos and/or measure yours carefully again to see if the 16mm would work. Or, failing there, you could learn to reflow your own emitters and just use the stock board. There’s a learning curve but it’s not terribly hard to do. Would recommend some good solder paste for that but it can be done with solder and flux (you’ll want separate flux, can’t rely just on rosin-core solder for this).

If board size/shape are workable with something normal or with some modification/shaping, you could even consider some of the small-die Osram emitters…very very throwy with narrow beams but I’m not sure how the beam shape would turn out in the reflector size you have in the light (could be amazing, could be mediocre or irritating, could also be less useful in a cave environment, imho).

Kaidomain also has these, bare and mounted, and they might have more choices, but sometimes the bins for their emitters are not as good as what Simon chooses and sources. Their Aliexpress store is called LHT Flashlight Store, pretty much the same items and prices as on their main website. Also worth a look at Richard’s offerings at Mountain Electronics if he’s got them in stock and you want faster domestic sourcing/shipping - his boards are excellent and he always chooses great emitter bins.


Thank you for the recommendations and links! The PCB is round, I think a 16mm would work but it might be tough to get centered.

I would be OK with low CRI on the thrower side. And where I live the caves are super tight so I pretty much only use the flood. A pencil throw would be fun for walking the dogs etc.

Should be doable…only 0.5mm gap and you could shim that with a strip of plastic or something if need be (normal good quality thermal paste, thin or thick, should give enough stiction to make centering the board pretty easy). I just looked up that light and it says only 180 lumens max, so given the emitter it’s really underdriving it (and reviews say little to no heat felt when running on high). I misread your post and thought the light was running 3 amps but in all likelihood it’s maxing at less than 1 amp. Sooo…color tint should still be pretty decent with the emitters I mentioned but it’s possible that they may look a tad warmer or have some green at that lower current (especially the SST20 although it’s a really nice emitter overall). I put an SST20 5000K into an old ultra-cheapie flashlight that runs 3AAA unregulated…added a 1 ohm resistor to limit it a little and actually at that current it looks decent. In other lights that have more modes which include very low currents, that emitter does get a tad greenish but that’s mostly white-wall observation and looks decent enough in normal use both indoors and out.

I guess I assumed they were driving it to 3A on turbo. 1A is a little disappointing. Are there any emitters with higher output at lower currents? LH315D?

Is it even possible to push 3 amp output with power coming from 4 x aaa?

These would be a slight improvement in lumens but more so in color and rendering. An XPL or even an XML if that would work with the optics might give a touch more but the tint would likely look a bit crappy. But still likely better than the stock emitters you’re used to. The better color might make it feel a little brighter even if the bump in lumens is so low that it’s technically not supposed to be noticeable (however, I sometimes dispute that…and dark-adjusted eyes may detect more output especially at the peripheries of the beams/beam types…but it won’t be much).

I couldn’t see any reviews that had current measurements. No idea if that uses a buck driver or a buck/boost, but probably the former? I’m sure with a boost it could go 3A at least for a little bit.

I think this would be a fun upgrade, maybe a learning experience, but probably for the cost of emitters and supplies you could look at an upgrade to a different headlamp (and a different cell if you’re not opposed to moving to lithium ion for this).

That is how I’m approaching it. I have a Zebra H600Fc MkIV that stomps this thing. The Fenix doesn’t get any use anymore so I thought I might as well play around with it a bit. I would also like to use it as a loaner when I take people caving.

Thanks for joining the gang, Gnarliest_Gnome!

Take a friend caving, give them memories that will last a lifetime…good plan! :slight_smile: I got to do a number of wild cave trips years ago, even spending the night in one in a region that was mostly undeveloped and still had a fair amount of unmapped areas inside. Had to drop through some holes in the floor, almost like someone had drilled them out for people, and belly crawl for a long way in an extremely tight low passage that was only about 20 to 24 inches high (had to remove packs and drag them beside us) but anywhere from about 100 to 250 feet wide. It was 18F outside but a nice balmy 58F underground. Many people will never experience such utterly still air and absolute blackness like deep in a cave…pretty incredible. Coming to the surface after almost two full days was like walking into the brightest light known to man. lol

I’ll be interested to see what you come up with and how the light looks with new emitters if you care to share later. Either in your thread or you could also add it to the What Did You Mod Today thread here: What did you mod today?

It sure can be wild underground! That sounds like a wild trip, especially not knowing what has and hasn’t been explored. I don’t think I’ve spent more than 8 hrs at a time but even that is quite jarring when you step out into the world. I’ve got a buddy who has been pushing me to rock climb harder things so it’s about time for me to “pay him back” with a good adventure.

I’m heavily leaning towards LH351D and SST20 combo. Right now looking at emitters from Convoy and trying to decide if I want tints to match and if I care about CRI in the SST20. Simon has the “dogfarts” in 5000k but his SST2O 5000K is low CRI.

I will definitely post the results once I’m done. Thank you so much for the help!

You’re welcome, hope it goes great!

You might like to see a fellow caver’s current project modding an old Petzl lamp. Old lights never die.