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Thread: Object/Subject Review: Prometheus Alpha XM18-B: Cerakoted

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    Default Object/Subject Review: Prometheus Alpha XM18-B: Cerakoted

    "Dark Sucks. Do something about it."

    Formerly known as "Dark Sucks", Prometheus Lights is a new custom flashlight business by Jason Hui, based out of California. Jason has shown a real love for making flashlights, back in early 2011 he announced he had bought a CNC mill and was going to start making lights full time. Now, the Alpha is his flagship light and his commitment to quality and constant improvement on the already great really make his work shine. This review is for the XM-L version of the Alpha, with a Cerakote finish over the normal electroless nickel plating he uses.

    Thanks to Jason at Prometheus for supplying the Alpha and Apprentice Package for review.

    I’ll be reviewing the Alpha in two sections: first, I’ll discuss the light objectively (the facts about the light itself), then I’ll discuss the light subjectively (my impressions about the light's performance when used for specific applications). This is a high-end EDC style light, so I'll be reviewing it as such. If you have any other specific applications you'd like the light tested for, let me know and I'll see what I can do.

    6-Minute Overview
    Below is a video "quick review" you can watch in just a few minutes, if you're not up for reading the full review right now:


    Manufacturer's Specifications


    Jason's philosophy on his lights is that any cost for packaging gets passed on to the customer, so he uses a minimal packaging to keep the cost of the light as low as possible. My review sample along with the Apprentice package and titanium zipper pull arrived in a box padded with paper.

    The light itself arrived in a simple cardboard tube with Jason's logo on the end, and the accessories of the Apprentice package arrived in this small drawstring bag.

    [EDIT: I've just been informed by Jason that this packaging is pretty new, and only the most recent lights shipped out have it. He has been getting a lot of feedback from customers that he should use packaging, so he's picked this packaging that will look good and still be cheap enough that he doesn't have to increase the cost of the light.]

    Construction Quality

    I'll say up front that the Alpha probably has the best quality feel to it of any light I've reviewed to date. This is a custom light, and while holding it you can feel the effort that's gone into designing this light.

    The Alpha is made from 6061-T6 aluminum, then electroless nickel plated. This leaves the light with a very shiny, reflective surface. Jason offers this in several different finishes so you can get your light to look just like you want. However, for my review sample the coating was taken another step, and a layer of Cerakote was laid down on top of the ENP. The Cerakoting is an extremely durable finish available in many colors, normally used on firearms and such.

    The Alpha uses one 18650 sized lithium ion battery. If you get one of the packages Jason offers with the Alpha, it will include one 2900mAh AW battery. The max current draw on here is just short of 3A, so even lower capacity LiCo chemistry cells should be able to provide full current without a problem.

    As a quick side note, Jason has given me permission to use this picture from his blog of an Alpha cut open from end to end:

    Let's take a closer look, starting at the head and working back.

    The Alpha is available with a choice of emitters: XM-L, MC-E, or XP-G in multiple color temperatures. This review samples uses a 4500K XM-L. The XM-L emitter is known for it's high efficiency and high output capability, and is mostly a "flood" type emitter. The Alpha is also available with either a faceted "Boom" reflector, or a TIR (total internal reflection) optic of about 20 degrees. This sample uses the boom reflector. The facets, apart from adding style, also serve to smooth out any rings or artifacts from the beam. You can see this effect in the beam shots further down. The glass lens has an anti-reflective coating on each side to ensure the maximum possible amount of light makes it through. Between the lens and the bezel is a blue fluorosilicone o-ring that keeps water from getting into the light. (Note: Jason has tested the Alpha to a pressure equivalent to 300ft deep for 5 hours, with no water entering the light).

    You can notice in the picture above a small marking on the side of the head. Below is a close-up:

    This is the "maker's mark", stamped onto each custom made Prometheus light, showing that it is in fact custom made.

    You can see the rear of the head tapers down to just slightly larger than the body diameter. The body itself has several grooves cut into it to give extra style and grip. The clip makes contact about halfway down the grooved section. The clip is on a ring around the light held down by the tail cap, and is very secure while still being easily removable without any tools (see removal details below).

    Here're close-ups of the grooves and the clip:

    As you can see, the grooves are very well formed. The clip is made from titanium (Jason offers heat anodizing to add some color for a few extra $) and has a cutout design.

    The tail cap features a recesses button, which is easy to press but maintains the ability for a solid tail stand. The button cover is available in orange, black, or glow-in-the-dark green. As you can see, Jason has left an area where the electroless nickel plating is still showing. The purpose of this is to add some style to the light, and also leave room for a possible metal switch cover upgrade in the future. You can see a close-up of the cerakote fade out in the picture on the right.

    Below are some pictures of the GITD switch cover in action:

    The two dark shots were taken at different exposures so you could get a good idea of what it looks like. What I usually see with my eyes is somewhere in between, closer to the picture on the right.

    Now, it's time to take the light apart!

    For general use, the light comes apart into three pieces: head, body, and tail. The clip comes off on the tail, but can be easily removed at this stage.

    The threads are thick and very well formed. Jason pre-lubes them with nano-oil before sending them out, and includes a bit of nano-oil for maintenance. These threads are extremely smooth. It's recommended to do battery changes by removing the head, not the tail. I've found this to make sense to me, as the larger spring makes battery changes more difficult at the tail.

    Also, you can see that the all the threads are non-anodized, but they are nickel plated, so they can maintain great electrical conductivity and still hold up to use over time.

    Inside the head you can see the circuit board sitting on a large copper tube. the copper tube acts as a heatsink, and quickly moves heat away from the emitter and circuit board to the body of the light, where it can be dumped into your hand.

    In the middle picture you can see the gap in between the heatsink and the rest of the head. This is where the body slips in and the head overlaps. This area is designed specifically to take pressure off of the threads and protect them in the case of impact or force applied.

    The picture on the right is a close up of the spring that makes contact with the positive terminal of the battery. You can see a small bit of solder has been applied to the end of the spring, to help prevent the spring from scratching up your battery. This design means that both flat-top and button-top cells will make electrical contact. I've tested with AW, Callies' Kustoms, and Trustfire cells, and they all work.

    On the left is a view down the battery tube from the head, and you can seethe serial number printed on a sticker inside. On the right is a view down the battery tube from the tail, and you can see the threads on the inside.

    This is the tail, featuring a McClicky forward click switch. A forward click switch means you can press the button halfway for momentary on, or press it all the way to click into a constant on position. From constant on, just click it again to turn it off. The McClicky switch is widely considered the best clicky switch currently available.

    This long spring on the end is a great feature, because not only does it help to absorb impact really well, but it allows you to fit a wide variety of "18650" sized cells in the Alpha. My Callie's Kustoms 18650 cells are actually more like 19700's (nearly 19mm wide and 70mm long), and they are a little snug, but they fit. I don't know of any common brand 18650 cells larger than the CK's.

    Here you can see how the clip sits just behind the o-ring. The o-ring keeps the clip in place when the tail is removed, but when you apply a little pressure the clip will slip off over it.

    Below you can see some shots of the light without the clip:

    Notice that the tail is still flush with the body, even with the clip removed. It's good to see that removing the clip does not leave a gap.


    This review includes the Apprentice package, which consists of a 2900mAh AW 18650 battery, clear battery tube with orange li, and XTAR single-bay 18650 charger. Prometheus also makes available a Journeyman package: Aprrentice package plus nano-oil, spare o-rings, o-ring removal tool, and all three button colors; and a Master package: Journeyman package plus spare lens, spare McClicky switch, and a cottonpickers mini voltmeter.

    The normal accessories (without any package added) include the clip, a small bit of nano-oil, two spare o-rings, a card with some stats for the particular light you receive, and now an instruction card. I did not receive the instruction card in my sample, but Jason sent me the file for it so I can refer to it upon request.

    All of the accessories (except the clip) came in the drawstring bag. The clip came attached to the Alpha.

    The stat card includes the serial number, CCT, emitter type, optic type, output at 30 seconds, and max drive current, hand written.

    The clip is made from titanium, and you can order it anodized for a few extra dollars. I found the clip to be very robust, while maintaining flexibility.

    Here you can see, the charger included in the Apprentice package is very minimalist, and fits the included 18650 cell just fine.

    Another optional "accessory" is the Prometheus Titanium Zipper Pull. Just like it sounds, it's a zipper-pull style bead made from titanium. These have currently only been made in very limited quantities, and you can choose your o-ring color along with some paracord, for a very stylish accessory for the Alpha. I'll post some more pictures of the Ti pull in post #2.


    User Interface

    The Alpha has a very simple user interface. The driver has 3 modes, Low, Medium, and High (in that order). You can cycle through modes by turning the light off then back on in a short amont of time.

    The Alpha has mode memory, so when you use a certain mode for a couple seconds, it will memorize that mode. After turning it off, the next time you turn it on it will be in that same mode. If you use a modes for less than a couple seconds, the next time you turn it on it will be in the next mode in the sequence. The memory persists through battery changes.

    For example, if I go to Medium mode and stay there for a while, then turn the light off, the next time I pick it up and turn it on it will be in Medium mode. If I then turn it off quickly (less than two seconds), the next time I turn it on it will be in High mode.

    For a look at the UI in action, see the video at the beginning of this review.

    Coming soon: a specific UI video

    Action Shots

    Light in Hand

    White Wall (Low, Medium, High)
    ISO 100, f/3.3, 1/10"



    Indoor Shots (Control, Low, Medium, High)
    ISO 100, f/3.3, 1"

    Outdoor Shots (Control, Low, Medium, High)
    ISO 100, f/3.3, 2.5"

    More Outdoor Shots (Control, Low, Medium, High)
    ISO 100, f/3.3, 2.5"

    More Outdoor Shots (Control, Low, Medium, High)
    ISO 100, f/3.3, 2.5"

    Mid-Range Shots (Control, Low, Medium, High)


    Submersion: I submersed the Alpha under a foot of water, turned it on and off several times, and left it under for an hour. After bringing it back up, I found no evidence of water entering the light or having affected it in any way. Jason has tested the Alpha in a water pressure equivalent to a depth of 300ft for five hours and it still worked.

    Heat: On medium mode, the light will get mildly warm, but there is no significant heat build up. On high mode, the Alpha will get warm quickly, and after about 15-20 minutes the head can become uncomfortable to touch. I fond I was about to hold the body comfortable indefinitely.

    PWM: By doing my normal test for PWM, swinging the light very fast and looking for dashes instead of a streak, I could not detect any PWM, neither can I hear any inductor whine on any mode. However, I have a more rigorous test. I set my camera to a shutter speed of 1/4000 second and point it at the head. At this short shutter speed, the light appears to flicker on low and medium mode, which means there is pulse width modulation used on these modes. I cannot find any way to detect the PWM in normal use, so you're not going to see it when you use it, but it is there. This is a much higher frequency PWM than I've seen in other lights with PWM.

    Drop: I dropped the Alpha from a height of about 2 meters onto several different surfaces, including grass, carpet, packed dirt, and wood, and there are no observable effects to either the function or even the appearance of the light. Jason performed a very rigorous impact test along with several other CPFers, and while sustaining visible damage the Alpha still worked (the video is available on his website).

    Reverse Polarity Protection: Because of the springs on both ends, the Alpha does not have mechanical reverse polarity protection. When inserting the battery backwards (negative end at the head) nothing happens, and the light works again when the polarity is corrected (positive end at the head). So, the Alpha does appear to have protection built into the circuit, but as always, I'd recommend not to push your luck, and just put the battery in the right way.

    Over-Discharge Protection: The Alpha includes a Low Battery Indicator flash, but it will not automatically shut off to prevent over-discharge of a battery. I recommend using a protected cell in the Alpha, but if you use an unprotected cell, the Alpha will warn you by getting very dim and flashing when the battery voltage gets low.

    Spectral Analysis

    All light that we see as white is actually made up of several different colors put together. The relative intensities of the different colors in the mix are what determine the tint of the white we see. For example, cool white LED's have a lot of blue, and warm white LED's have more red or yellow. This measurement was done on a home made spectrometer. Note: the peak in the 900nm region doesn't really exist, it's a piece of the second-order spectrum that's showing up here because of the high intensity of the light source.

    Output, Current Draw and Runtime

    Note: For this light, you'll see the manufacturer's claimed output is higher than listed in the specs above. Jason rates his lights at the lowest possible output for the range possible in the emitter bin he uses, then includes a card with each Alpha stating the max output he measures from that specific light. So, he claims a minimum of about 450 lumens from an XM18-B, and he measured my specific sample to have a max output of 489 lumens. The medium and low mode claims are 30% and 5% of max, as claimed by the specs for the driver.

    Current draw was measured at the tail cap using a fresh AW 18650 3100mAh ICR battery. ANSI runtime ratings are the time it takes for a light to fall to 10% of it's original output.

    Note: The vertical axis of this chart represents a relative brightness measurement using a home made light box. The horizontal axis is time in hours:minutes:seconds. Runtimes are stated in hours:minutes:seconds. These graphs are truncated to show detail.

    Another Note: these runtimes were taken using a 3100mAh AW cell (for consistency with my other reviews), the cell provided in the Apprentice package is a 2900mAh AW cell, so you can expect slightly shorter run times if you use that cell.

    Mode Comparison

    I did not show the full extent of the low runtime on this graph, so that you could more easily compare the medium ond high modes. To see the full plot of the low mode, scroll down just a bit.


    Time Regulated: 1:04:15 (approximate)
    Time to 50%: 1:08:00
    Full Runtime: 1:08:00

    [EDIT: After receiving some feedback that my plots weren't quite as flat as might be expected, I re-ran my test on High mode with some slightly different conditions. Normally, I use a 3100mAh AW battery in all my reviews to provide consistency, but just to be safe I ran a test on High with the 2900mAh AW battery included in the Apprentice package. Also, I normally run a fan on the light to cool it during a test, but my equipment is kept in a room without air conditioning. So, to see if the heat was affecting the output I moved my equipment into a room with air conditioning. The trials noted with a "+ Extra Cooling" are the two new ones, done in the room with air conditioning. You can see the regulation is noticeably better when the light is kept cool.]


    Time Regulated: 2:29:59 (approximate)
    Time to 50%: 3:52:32
    Full Runtime: 4:07:18


    Time Regulated: 9:27:38
    Time to 50%: 25:10:24
    Full Runtime: 26:41:04

    At the end of each test, the Alpha has a sharp drop in output, then quickly activates the low batter indicator flash. During this time, the light is very dim, and it flashes off once every two seconds or so. It will continue doing this for several hours if you let it, but it is important to recharge the battery at this time, or ideally before the LBI activates. It's not healthy for a lithium ion cell to be deeply discharged. Try to charge your cell before the LBI turns on, but definitely stop using the light when you see it start flashing. It won't be too bad to do it once or twice, but don't make a habit of letting your battery get that low.

    Subjective Review


    Quick break down:

    +A piece of art as well as a tool, very stylish
    +Incredible durability
    +Attention to detail
    +Great brightness, great options for emitters
    +Several beautiful finish options
    +Great beam pattern
    +Clip easily removable without tools
    +Perfect switch feel
    +Accepts flat-top cells
    +Low battery indication

    -Low and medium are slightly too high
    -Regulation could be better
    -Click-to-cycle-through UI
    -No lock-out
    -Only accepts an 18650

    The two main highlights of the Prometheus Alpha are it's style and quality construction. This is a light that will be very durable, and look good doing it. This is one of the few lights that my wife isn't embarrassed for me to carry, because it looks so good. Jason has paid great attention to detail, and it's paid off in the Alpha. I've also been impressed with his commitment to continually improve his design. For example, the McClicky switch current uses a standard spiral spring, but Jason has been experimenting with a new wave-type spring that will provide a better electrical connection by shortening the path from the battery to the switch.

    I really like the beam pattern on the Alpha, the faceted reflector is fun to use. At one point Jason had an aspheric lens available for the Alpha, which could make this really great as a thrower, but his source for those no longer has them available, so we can hope he finds them available some place else.

    I really like the clip design. I'm seeing similar things on more lights now where the clip is held down by the tail cap, but this is the first one I've seen where the clip is on a ring that goes all the way around the light, making it extremely secure. The act of removing the clip is also the smoothest I've seen on the Alpha.

    The McClicky switch is also my favorite click switch I've used. It turns to momentary on at a very slight pressure, and has just the right amount of travel before clicking into position. The click itself is firm and satisfying, without being gritty or loud. The only disadvantage here is that the Alpha has no lock-out mode, because the threads are electrically conductive all the way though. This means you can't slightly unscrew the light to prevent accidental activation, so if you're going to be storing or transporting the light and need to be sure it won't turn on you need to remove the battery. The recessed button should be sufficient to keep it from coming on during average pocket use (I haven't had any problems with this). At the very least, the Alpha is bright enough that if it does turn on, you're probably going to notice.

    On that note, just my personal preference, but I would prefer the low and medium modes to be moved down just a bit. This would make the Alpha useful for a lot more conditions. I'm not talking about a super low, but a slightly lower low would mean much more run time, which would greatly benefit the Alpha.

    I really like the low battery indication on the Alpha. The light maintains a goot brightness throughout most of the battery life, and when the battery gets low the light gets very dim and starts to blink. I prefer this to a light that will automatically shut off at a certain point, just because I'd rather tell my machines what to do then have them tell me.

    [EDIT: I re-ran some tests on High mode with some extra cooling, and found that the regulation looks a lot better, maintaining high brightness for longer. See the note and chart in the "Performance" section above.]

    One significant drawback is that the Alpha is only approved for use with 1x18650 battery configuration. The driver can accept up to 6V, so theoretically you could pop in 2xCR123 without overloading the driver, but Jason's recommendation is that that would be too much power for the emitter to handle. I love rechargeable batteries, and use them almost exclusively, but for me to truly rely on a light I want to be able to throw in primary batteries in an emergency. On a good note, the Alpha seems to be able to accept pretty much any size of 18650 battery I throw in it, including my Callie's Kustoms, which are often too big to fit in some lights.

    [EDIT: I got some info from Jason on CR123's in the Alpha. Basically, the driver and emitter can handle CR123's just fine, but the batteries themselves can't handle the high current drain. The official stance on CR123's in the Alpha can be found on this page. Basically, pulling almost 3A from a CR123 has the possibility of leading to thermal runaway and explosion of the battery. It might be possible to use them in an emergency on medium or low mode, but it is not recommended.]

    My only other main dislike of the Alpha is that it's UI uses a click-click-click to cycle through modes, and it doesn't always start in the same mode. While using the Alpha for a period of time, turning it on and off, I like that it remembers the last mode I used and comes back on in that mode. However, when I pick it up the next day, I don't remember what mode I used last, but the Alpha does. This means when I go to grab my light, I'm not sure what mode it's going to turn on in. My personal preference is that we get completely away from clicking a light on and off repeatedly to change modes (that was great for time, but we can do better now). However, that's something for future Prometheus lights. For the Alpha, I'd like to see the UI just tweaked so that if the light isn't used for a long period of time (maybe half an hour to a few hours?) the light forgets the last mode used and defaults to starting in low. I don't know if this is possible, but it's what I want.

    Overall, I see the Alpha as a great entry point to the world of custom lights. You can get one of these for $225 and have an excellent custom light, with your choice of emitter, reflector, finish, even switch cover color. I'd like to see improvement in the UI and the regulation, but with the commitment to excellence that Prometheus lights has already shown, I have no worries here.


    The Alpha, running off a single 18650, is a good candidate for every-day carry, especially for those of us in situations where we need something that looks good. With the choice of an ENP finish, you can have something that looks very stunning and is going to draw a lot of positive attention. With the Cerakote finish, you're going to have a light that can take a beating and still look really good.

    The Alpha meets most of what I look for in an EDC. Primarily, the size is a little larger than I like for an EDC, but it's definitely doable in large pocket or a small bag. There is also (in limited availability) a "shorty" body which will take an 18350 or 16340 sized cell. The Alpha has a wide range of modes, which means you can use it for several sorts of tasks. As I mentioned, I'd like to see medium and low be slightly lower, giving the Alpha a better spread, but as it is it's still a great choice. With the boom reflector, the Alpha is pretty floody, which is my personal preference in an EDC, given that the majority of tasks are going to be easier with more flood than throw. The 18650 size is my preference for EDC because of the high capacity and power available, but I do prefer an EDC to accept primaries in a pinch.

    Overall, the Alpha would be a great choice for your EDC, and it's going to be one you want to show off.

    Long Term Impressions

    I'll fill this part in after carrying the light for a while. If nothing get's added here, either I find nothing else worth noting about the light, or I end up not using it often.
    Last edited by Bigmac_79; 11-16-2014 at 08:25 PM.

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