Review: Prometheus Lights Alpha Series XM18-B (XM-L T5 4C | 1x18650)

Please do not hit the refresh button on your browser... this is indeed a review of Prometheus Lights' Alpha XM18-B and yes, that is indeed a picture of a bowl of noodles.

Specifically, it is a bowl of spicy Shin Ramyun (one of my favorites). Ramyun (or ramen [Japanese] / gong zai mian [Chinese]) is the proverbial fast food delight of many Asian cultures that really couldn't be simpler or quicker to make, thus living up to its "Instant Noodles" billing. Never mind that it provides you with nearly the entire recommended daily intake for sodium in one serving (most packages have about 1800mg), it is a delectable foundation with which you can build the perfect meal upon by garnishing it with eggs, vegetables, meat or seafood and supplementing it with side dishes. These will only serve to complement the unpronounceable exotic "ingredients", with disodium guanylate, disodium inosinate, disodium succinate just to name a few.

With that said, there are subtle but important steps involved in making just the right bowl of ramyun which my wife's hal muh nee (grandmother in Korean) had perfected. If you add too much water then you dilute the soup base and it comes out tasting bland (my tastebuds cry out for every last bit of that disodium watchamacallit ingredient); overcook it and the noodles are mushy soft, likewise leaving it around for too long would allow the noodles to absorb too much water causing the same problem but with less soup. As age and health issues set in, it was one of the few meals she could easily whip up when we visited. Despite our protests that she shouldn’t bother and to get some rest, she insisted and would meticulously prepare each bowl as if it were for royalty; the soup was always just the right amount of saltiness; there'd be well beaten eggs that created just the right amount of "fluff" upon hitting the boiling water and had great texture and flavor due to the perfect blending of the yolk and egg white; and last but certainly not least, the noodles were ALWAYS al dente! Bottom line is that her attention to details is why we could just about taste the love she poured her heart into preparing this humble meal.

I've had countless other bowls of ramyun since she passed on but it's something I've not quite tasted again…

Jason Hui (designer, fabricator, strategist & founder of Prometheus Lights) on the other hand may not have the same zeal for making ramyun but what he does share is an attention to details and loves, in his own words “…to make ideas real”. Fortunately for us flashaholics, one of those ideas was a dive light which in turn led to variations of other lights and eventually birthed the Alpha prototypes. At that point he didn’t have any CNC machines, just a manual lathe and mill. That changed just over a year ago when he found an awesome deal on a very old Haas CNC mill. It was born at the Haas factory in Socal, lived its life in New Jersey for about 20 years, and then came all the way back across the country. Jason basically said to himself, “if you buy this machine you are in the flashlight business...” so here we are. This review will cover as much about one of his ideas turned to reality as well as the man behind it.

Note: Ti clip & Ti zipper pull are optional accessories

MSRP: Light only - $225 USD and up | Apprentice Package (this review) - $255 USD

“Packaging costs money, and this gets passed on to you, the buyer. It also (likely) means that it won't fit into a small USPS flat rate shipping will be more expensive.”

Jason is debating use of premium packaging and until he sorts that out, for now, he ships his lights in a standard USPS flat rate box w/some paper material for cushioning. The items arrived as such:

He dubs the package he sent “The Apprentice”, which includes (beyond the light):
- 1 x AW 2900 mAh battery (that comes in a nifty little carrier that can be used to carry a spare)
- 1 x XTAR MP1 charger
- 1 x maintenance package consisting of 2 x spare o-rings and a small bottle of Nano-oil (this is not normally mentioned as he likes to throw it in as a surprise for his customers but I was authorized to disclose this spoiler)
- a report card on which he personally records by hand the following information for each light:

The apprentice package is great for budding flashaholics who don’t yet have a battery/charger and ensures they are able to enjoy immediate use of their light as well as doing basic maintenance in the long run.

If you don't have time to read through all the details (although I highly suggest you do ^_^) you can watch this quick summary video (but doesn't go into the depth that this review provides): ]

"I enjoy a good metaphorical name from time to time like the gladiator, super nova, or death star...but they are meaningless."

An alphanumeric nomenclature was utilized for Jason’s lights as he feels it allows easy identification as follows:
- the first two letters identifies the LED in use (XM = XM-L, MC = MC-E, etc)
- the next two numeric characters denotes the battery size/type (18650’s thus far but he now has a shorty)
- the final letter identifies the reflector or optic in use (B for Boom)

In the case of the XM18-B, it features an XM-L LED powered by one 18650-sized battery and utilizing a Boom reflector:

"Everyone anodizes, very few EN plate. I want to be different..."

Electroless Nickel plating is a rather unique finish as far as flashlights are concerned and the XM18-B is the only one in my current collection to feature it. The EN plating process is auto-catalytic; that is, it adheres to the substrate it’s applied to without the need/use of a power source (unlike anodizing). The advantages it offers over anodizing is that it allows for uniform application even over complex shapes/curves and is slightly harder. The disadvantages though are; it’s heavier, will increase the OD (outer diamter) of the object being plated and fingerprints badly. EN plated surfaces are still electrically conductive thus doesn’t require the removal around areas where it’s not desired (e.g. tubing ends), however, this also means that the XM18-B cannot be locked out at all.

There are currently three finishes available for standard Alpha series lights. I received a Stone Wash finish which, as its namesakes implies, is like a smooth stone and encompasses the entire outer surface of the light with the exception of the seven circular grooves:

Subjectively, it’s an attractive finish and in conjunction with the EN plating that is slightly warm in color*, lends a distinct character to the light. However, EN plating will not cover any machining marks which Jason intentionally leaves behind as he likes to "...retain some evidence of the process". I suppose though that being a one-man setup, economics come in to play as well as it would take additional time and added cost to buff out every single mark.

*see comparo pic of shorty tube version vs. SS SolarForce in Size/Handling section

Each light features a UCL lens and upon first glance, I thought a lens wasn’t installed. It truly is that clear and non-reflective albeit, I don’t know if it’s specific to this particular lens, the type of AR coating used or a combo of both in conjunction with the boom reflector:

There are seven circular grooves that serve as the only aesthetic element on the body:

The tailcap features a recessed black rubber cover of which underneath lies a McClicky switch:

This allows for tailstanding without any issues:

"…design for disassembly and repair."

This is a main principle that Jason follows with the build of his lights. A bit of time, thought and revisions went into the mounting of the driver. He finally ended up with an implementation that was both aesthetically pleasing and still allows easy removal by either him or if so inclined, his clients:

The notch allows one to stick a screwdriver in it to easily dismount the driver:

As a prime example of attention paid to details, Jason places a blob of solder on the spring tips which is further sanded down to prevent the sharp cut-off from scratching up the batteries:

Neither my shortest cell (AW IMR 1600 @ 65.2mm) nor longest (XTAR 18700 @ 69.2mm) had any fit issues:

Overall, it's a sleek, minimalistic design that is more organic in nature and offers a nice break from the standard tactical/tacticool fare.

With very few exceptions, flashlights are designed to cater to the male-dominated market. Beyond the SureFire Isis, I'm not aware of a light that was purposely designed with the fairer sex in mind (and no, an existing light with bright colors doesn't count). While I can't say it was Jason's intent, I personally find that the Alpha series lights have a unisex appeal to them. My wife agrees as well and the XM18-B is one of the few lights that has caught her interest and elicited comments beyond the typical “That’s nice dear…” when asked for her opinion.

Case in point, it can look manly when clipped to the exterior of a Maxpedition Fatboy and boldly displayed (scratches and dings be damned!) or decidedly feminine nestled within a LV Artsy MM (especially when adorned with a trinket of choice):

My wife doesn’t like to carry any large, heavy items so the shorty tube will be her preference for those times I insist she carry a light for “just in case” purposes:

Besides, it's one of the few lights that she'll actually carry that would fit in her clutch.

While it hasn’t become her EDC (she prefers AAA-clicky format), she has “borrowed” it every so often and finds the neutral tint to be quite pleasing and useful when picking out her clothes in the wee hours of the morning without needing to hit the lights to disturb anyone.

As can be seen above (exposure locked between L/R pairs and on AWB), the floody profile of the beam and the tint in particular has enabled her to keep the XM18-B on low (vs. med for Mr. Elfin) and has been a boon in helping distinguishing between the many different shades of her jeans (I don't ask her why she has so many pairs, and she doesn't ask me why I have so many flashlights... peace reigns supreme! ).

I often see threads requesting suggestions on gifting a light for a female recipient so perhaps this is one to keep in mind if said recipient is as particular about her style preferences as my wife.

“I've deliberately stayed away from 123 (battery size) lights because these are quite common.”

L to R: RL3100 | Sunwayman T20C | Xeno G10v2 | Prometheus Lights Alpha Series XM18-B | FoxFury Rook Checkmate | ThruNite TN11 | Lighten7 Elite M1B | Lighten7 Elite M1A

The XM18-B runs about mid-pack among the 1 x 18650 sized lights in my collection but fits well in my medium-sized hands:

The smooth finish means it’ll be more likely than not to create problems with grip under wet conditions or when wearing certain gloves (especially those made from cloth). Also, given the switch is recessed, I needed to grip the light further towards the end so that my thumb can fully depress the switch.

[NEW 5/16: The weight of the light in this config is:

Head - 2.42oz (68.7g) | Tube - 1.83oz (52g) | Tailcap (without clip) - .54oz (15.4g)

For a total of: 4.79oz (136.1g)

The Ti tailclip weighs .07oz (2g)]

While the Alpha series was initiated on a 1 x 18650 platform, late last year, Jason started producing “shorty” bodies that can accommodate both 16340* (w/the included sleeve) and 18350 cells. He recently put up a limited run of five of which I snapped one up to include in this review.

*Given the current draw of 2.8A on High, one should only use IMR cells.

With the shorty tube installed, it transforms the light into one that is EDC-able (at least in my book):

L to R: AW IMR 16340 | UF 18350 | SolarForce L2M SS SE (note the cool color of this SS light vs. the XM18-B) | SureFire L1 | Prometheus Lights Alpha Series XM18-B w/shorty tube | SureFire L4 | SureFire G2Z

This adds to the overall versatility of the platform and allows a full length tube when extended run time is desired and a more compact form for better portability at other times.

[NEW 5/16:
The weight of the light in this config is:

Head - 2.42oz (68.7g) | Tube - 1.17oz (33.1g) | Tailcap (without clip) - .54oz (15.4g)

For a total of: 4.13oz (117.2g)]

I don’t yet have an IMR 18350 but grabbed an old UF one (that is actually 37.4mm long) for testing and found that this particular cell created an issue in that once the head was completely tightened, the light wouldn’t turn on. Once I loosened the head about ¼ turn then the light came on. I haven’t isolated the issue yet but something to keep in mind in case you happen to have these cells.

I didn’t encounter any such problems using an AW IMR 16340 (the only 16340 cell that should be used given the high current draw this light is capable of). With the sleeve in place, I wasn’t able to induce any battery rattle regardless of how hard I shook the light.

An additional point I’d like to highlight is that the size of the ID of the tailcap-end of the tube is smaller than the OD of the head-end thus one couldn’t simply attach the shorty tube as an extension to render it 2 x 18500 capable.

“One thing that sets my lights apart is attention to every possible detail.”

Based on various correspondence with Jason, it’s evident he sets a pretty high-bar for both himself as well as his creations and is often not easily satisfied until he tweaks something until it can’t be tweaked anymore (I’d recommend reading his blog for examples). His pride of craftsmanship is only tangible in how it translates into his customers’ pride of ownership. If other Prometheus Light owners’ units are like the sample I received then they should likely be pretty proud since the XM18-B is one of the best lights I’ve tested quality-wise (and I have tested my fair share).

I’m hard-pressed to find anything to fault. Features that ostensibly are purely for aesthetics at first blush are in fact intentional;

- the blue o-ring offers a striking contrast that begs for attention. However, looks aside, this o-ring is fluorosilicone based and costs considerably more than standard silicone o-rings. It offers excellent extreme temperature/weather properties, compression set resistance, fuel oil resistance (thus used in aircraft fuel systems). It does however have poor abrasion resistance but no worse than standard silicone:

- geometry comes in to play with a strategically milled taper towards the end of the head:

This was by design to prevent direct pressure (with the light laying flat) from being applied to the threads that reside directly on the inner diameter opposite of the taper thus greatly minimizing the chances of incurring any damage to them:

(pics re-used w/permission)

- another engineering decision applied to the head is that it is milled as a single piece with a solid band of material right aft of the reflector that greatly aids in both structural strength and heat dissipation:

(pic re-used w/permission)

- the level of details is no less on the tail end, again with geometry invoked (vis-à-vis the absence of uneven shapes) coupled with the raw strength of the material to help prevent crushing:

- the point where the tailclip meets the body with either tube falls on a raised surface and not a groove

The EN plating offers pretty effective natural lubricity with a coefficient of friction of EN on EN at .45 unlubricated and .2 lubricated (lower is better - source: Wikipedia). With the Nano-oil applied to the threads, the best way to describe the twisting of the head would be that it’s akin to rubbing two steel ball bearings or qigong balls together. It’s not quite as smooth as say anodizing on anodizing but subjectively has a satisfying feel that to me, conveys a precision fit.

With that all said, here are a few nitpicks I did manage to find:

  • I was able to induce some battery rattle with the AW IMR 18650, but ony by shaking really vigorously. However, this is really par for the course for newer lights given the ever growing 18650 battery cells (that are really no longer 18x65) and thus the need to accomodate the larger sized cells in this format
  • there is a very faint buzzing noise from the McClicky in low mode that becomes slightly more pronounced in medium mode; this is regardless of the tube or battery is in use
  • I’m able to induce a rattling noise with the McClicky switch when it is depressed (on) but apparently, this is inherent to all McClicky switches and not particular to Jason’s build (McClicky owners, please feel free to chime in)
  • the switch on my unit was actually installed pretty tight thus requiring the use of a plier to remove it

In specific regards to the finish, while the bulk of machining is done by CNC there is still a lot of manual hand work involved as such, there may be some minor cosmetic imperfections that Jason intentionally leaves behind as previously mentioned:

Again, if you are looking for a cosmetically perfect light then you may wish to pursue an alternative finish/coating or perhaps even a bespoke model.

“My philosophy is that simple is better.”

There are 3 modes (L – M – H ) that can be accessed through the tailcap switch. Given it’s a forward-clicky, momentary use is possible. The last used mode is memorized provided the light is left-on in that mode for at least 2.5 seconds (please see [forthcoming] video review for further explanation). This is also retained through battery changes as well. In-line w/his philosophy, there are no extraneous modes to cycle through.

As of May, I’ve revised the calibration for my PVC LMD as follows:
- To measure lights with claimed output < 400lms, I’ll set the Xeno G10v2 on Med mode (180lms), set Extech HD450 to 400 range and calibrate sensor for 170lms
- To measure lights with claimed output > 400lms, I’ll set the Xeno G10v2 on High mode, set Extech HD450 to 4K range and calibrate sensor for 465lms after the output settles down (approx. 3-5 mins)

[to come]

[ to come - for now, please see "THROUGH A DIFFERENT LENS..." section for a few pics of tint comparo vs. cool white light]

Indoors (5m)



For details of the above indoor shots and comparo vs. many other lights, please check Epic Indoor Shots Trilogy

Whitewall Hunting
Exposure settings sequentially from top left: 1/25, 1/100, 1/800, 1/1600 @ f2.9 on AWB (light is ~.4m to wall / camera ~.59m):

The relevant battery stats are provided above each runtime graph along with:
- Voltage of the battery at the start and end of the test
- Current draw as taken right before the test
- Actual runtime using ANSI FL1 (first in HR and then in M so for the AW2900 read this as 1hr OR 62min)
- NEW (as of May 2012): Lumens measured on PVC LMD @ 30 seconds
- Also for High, captured the temperature: ambient, the head at start and the max it reached (fan was used for all bats)

Using the AW2900, I slighty topped the claimed runtime of 1hr on High. This light is driven hard and while it has good heat dissapation, care should still be taken when using it continuously on high mode.

I will post results of other modes when completed but going strictly by on paper calculations using the current draw measured with AW2900; 867mA for Med & 128mA on Low, the runtimes should be 3.3hrs & 22.6hrs respectively.

NEW 5/15: While I wait for my AW battery order to arrive, I've conducted runtime w/shorty tube using the following cells. I suspect my AW IMR 16340 is no longer good as it's gone through many deep cycles so will look to rerun that in the future but for now, here is what you can reasonably expect with these cells:
NEW 5/16:
The AW IMR 18350 arrived and I just wrapped up the runtime and was able to squeeze 16min out of it before the low voltage warning kicked in. As you can see, the light was able to draw nearly the max current and thus able to stay in nearly flat regulation with the highest output for the entire run as compared to the other two cells. However, with the increased current draw comes higher temperature and max achieved was 117.4F, definitely nor recommended to run this light unattended/uncooled for long stretches.]

The XM18-B is a solid piece of old-fashioned hand-crafted goodness and quality-wise, is one of the best lights I’ve had the privilege of testing. It has been well-thought out, well-executed and where possible continually improved upon.

An uncertainty remains with the durability of the EN plating. It’s my first experience with a light that features it and only time will tell how it holds up. There is also the matter that Prometheus Lights is still a relatively young and small company without the lengthy track record of some of the larger players in the industry. However, if the XM18-B is any indication of the level of quality and thoughtful engineering we can expect from Jason’s products then I’m optimistic that he should be around for a long while leaving his maker's mark on his creations.


  • outstanding build quality with attention to details evident
  • use of boom reflector creates very nice floody smooth beam free from discernable artifacts and without abrupt transition from hotspot to corona to spill
  • EN plating offers a distinct look that doesn’t scream “Me too!”
  • available shorty tube adds flexibility to platform


  • will get hot if used continuously in High mode
  • smooth finish = slippery when wet
  • uncertainty of long-term durability of EN plating
  • lack of long term track record for this relatively young company


  • true XM16-sized variants


XM18-B and apprentice package provided by Jason Hui, Promethus Lights for review



gorgeous pics as always , i hate to see how much .

any links or...

oh N/M i just seen the price, still very nice build . and now i am hungry for noodles

God damn that ain't no budget light.

Ceci n'est pas une budget light...

This being Budget Light Forum and all... :P

Still looks nice at least.

Awesome review and pics there turbo!

All we need is the link to those stainless steel chopsticks.

Now time to order some pho. :bigsmile:

nothing wrong with broadening the range of lights discussed here on BLF. the more the merrier.

hum........... do i get an employee discount?

just kidding.

very nice light.

That's a piece of functional art.


Beautiful light! I thought I recognized it from "". I greatly admire Jason for his dedication and decision to bank it all on the light business. Oh, to have a CNC machine!!!

What's the website?

Cool zipper pull also. Is it tritium? Where is it from if I may ask?

Thx guys!

To learn more about Jason's creations (including the Ti clip & Ti zipper pull) please visit his site:

@taz, those are GITD o-rings, however I recall that he might be working on tritium ones. Feel free to contact him.

Ceci n'est pas une pipe non plus

I appreciate Jason's work very much and would really like to support his business, but i can't wrap my head around shelling out so much for a 3 modes chinese driver aluminium light(You can have the same tool for 20$ shipped...), hand made with pride or not.

To coin a much overused phrase
Dear Santa…

Excellent story and review .

LOL…that’s why you are on BLF, not CPF

the price is actually kind of reasonable considering that it is pretty much a hand made light.

i think the one thing that really hurts the Alpha's desirability is that it doesn't offer any functionality that i can't get from something significantly cheaper. SF L2p + intl-outdoor 3A dropin = about $45 for similar performance from an equally handsome light.

does Jason offer custom modes? that's one thing that would make his light different from cheaper alternatives.