Frelux Synergy 2 in depth review (LH351D, 14500, Made in the USA)

Today I have a special light on my review table, the Frelux Synergy 2. If you are a long time subscriber you may remember that in October of 2018 I reviewed the original Frexlux Synergy 1 side-by-side flashlight. The Synergy 2 is the larger big brother and brings lots of new improvements and upgrades to the side-by-side format, and is almost entirely made in the USA. Let’s settle in for a longer review and look at the Synergy 2.


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Packaging for the Synergy 2 is a custom made cardboard box. It’s basic, but neatly done with just the Frelux logo and slogan on the top. The inside flap has a quote and a US flag to remind you the light is made in the US. Inside, the light is protected by a laser cut black foam protector. Accessories are a Frelux sticker and little quick start manual with a link/QR code to download the full manual. 


Construction and Machining

The Synergy 2 is made from US sourced 6061 aluminum. It is offered in a large variety of anodizing colors with Black, OD Green (what I have here), and a blue being the core colors at the time of review. The clip is made of grade 5 titanium and is also available in  raw, gold, and blue colors. 

It’s a side-by-side battery design, with the batteries in a parallel circuit. At the front of the light you have two brass contacts that have physical reverse polarity protection provided by a circuit board surrounding these contacts. The result is a light that’s a little picky on 14500 batteries if you decide to run those. Button tops are required, and watch the diameter of your cells too. Frelux has a list of tested batteries that are known to work with the Synergy 2, and it’s probably best you stick to those. VapCell’s 1100mAh models seem to be the best option (14.09mm). My 800mAh Keeppowers (14.41mm) were a bit too large in diameter.

The Internal Construction is a neat design; you have a brass threaded rod spanning the length of the light that threads into the head section, goes through the middle and tail section, and then the tail nut tightens everything in place and provides compression on the o-rings on each section to provide water resistance. The switch up front is an electronic switch, but it’s a very satisfying feeling too; it’s solid and crisp. The switch also has a mechanical lock feature which I recommend using during carry. Just rotate it clockwise and the button physically can’t press the e-switch. There isn’t any visual sign it’s locked, which is a little disappointing, but it’s an effective solution and keeps the UI simple. The Synergy 2 doesn’t carry a formal water rating, but Ben has tested it in a 8ft column of water overnight without a problem, so it should be ok in most situations. 

The tail brings the light all together; externally it has a nice USA engraved on one side of the black button and the battery orientation diagram on the other. The tail nut is a cool piece it’s what holds the entire light together and holds the clip on the light (along with the dovetail) during battery changes via an o-ring, which is a nice improvement over the Synergy 1. Internally there is a circuit board with three springs-two for the batteries and one for the brass center rod.



One of the reasons why I enjoy this light is all the machining content that is shared on the Frelux Instagram page. I am a want-to-be machinist. I enjoy watching several YouTubers make stuff, and just want a machine to play with. Ben of Frelux produces these lights in his home shop with a Brother CNC machine. Make sure you check out the video version of this review for some of this machining footage.

What’s somewhat unique here is how he has setup the 4th Axis on his machine along with the four sided pallet design, to maximize his machining times and get the most work done per cycle. With the pallet design it’s almost like a 5th axis machine. He designed a tool that mounts in the mill to allow the mill to rotate the parts in the fixture and continue machining without human interaction. The Synergy 2 took all of this into account during the design process. It allows him to maximize his time while the CNC is running to get the next pallet of parts ready and do other finishing and assembly tasks. The end result is a light that was designed with production and keeping the overall final product affordable in mind. All tumbling and anodizing is done in house for tighter tolerances on quality. Even the soldering of sub components, finish assembly, packaging, and shipping are done at the Frelux headquarters. 


Size and Weight

I measured the overall length at 95mm, width at 41.6mm, and thickness at 21mm not including the clip. Weight with Vapcell 14500 batteries is 6oz or 170g. This makes for a decently heavy light for its size and material. This design inherently has more material left after machining than a typical cylinder light. More aluminum could be removed through more complex machining internally, but it would greatly add to the complexity and overall cost. As far as competition there really are not many other side by side AA lights on the market to compare it to, so can we say class leading? 


The retention of this light is interesting. I have to first start with the size and how that impacts its pocket carry. I enjoy carrying a 14500 sized light, especially in warmer months as I wear more shorts. Since cargo shorts are no longer fashionable or accepted in my house, the result is less pocket space and an EDC to suit. With jeans it’s a bit of a different story. I find that despite the added width of the side by side format, there is still room for the light in my left front pocket and my phone deeper down in the jeans pocket. It’s too big for the coin pocket that you typically find on the right front side of many jeans. This is where the Synergy 1 was just about the perfect size.

That said one of the Synergy 2’s new features is it’s tension adjustable pocket clip. This is a neat design, the clip is retained in a dovetail in the tail section and then the tail nut that holds the tail section on to the light controls the clip’s ability to slide closer or further away from the body, thus setting the tension. It can be very tight or fairly loose, so it’s adjustable to a variety of different pocket materials. That said the very end of the clip isn’t flared out much so it can sometimes be a little hard to get started onto a pocket. Frelux does include a small adhesive vinyl sticker to place where the clip makes contact with the body to help prevent excessive wear on the anodizing. It’s a nice touch but I wish more then one was included in the package.


Grip in the hand is still fairly comfortable. If I choke up a bit I can still get all 5 fingers on the light. It’s a kind of modified pistol grip, if your thumb is on the light jimping on the top, the jimping on the bottom ends up fitting well with my middle finger. I do wish the jimping was slightly deeper and a little more aggressive. 

LED & Beamshots

The Synergy 2 is using a Samsung LH351D LED at 5000k and 90 CRI. This is a great emitter in my opinion and is quickly becoming one of my favorites that’s in current production. It’s a nice combination of tint, output, and high CRI. It’s surrounded by a smooth fairly deep reflector, with an anti reflective coated glass lens on top. There is just a hint of tint shift in the very center of the beam. I only noticed this when shining it at full power onto a white surface, it’s not noticeable during real world use. The resulting beam does have a pronounced hot center and ring at the edges before you get into the spill. Practically this isn’t a bad thing and the deeper reflector helps the light throw better than I initially expected. That said, I would prefer to see an orange peel reflector to smooth that transition out a little further.

This light is using a driver that Frelux had designed specifically for this light and it’s circuit boards are produced and populated in the USA. It has a ramping UI that I will speak more about here in a minute. The light is capable of running on the three most common chemistries of AA sized batteries. Standard Alkaline batteries, Ni-MH producing a maximum of 250 lumens, and Lithium Ion 14500’s producing a maximum of 700 lumens. The driver features memory, Low Voltage Protection(LVP), and temperature protection as well. No PWM was noticed with either battery type. 


Heat and Runtime

I ran three runtimes a few times with this light to see the differences. I focused on rechargeable batteries since that’s what most people will run this light with most of the time.

For my test with 14500’s (Lithium Ion) I used 2x VapCell 14500’s. Mine happened to be flat tops which won’t run in this light, but thankfully some small 1mm magnets worked to get around this until my button tops arrive. I got three minutes of the highest output before this light stepped down due to thermals. As you can see the heat continued to increase here but everything was pretty tame, peaking at 33.4C (which is basically body temperature). It’s a safe temp, almost too safe, as I would prefer a bit longer runtime for a little more heat. From there the light ran at 42% relative output for 2 hours and 13 minutes, before stepping down to about 18% relative output and running for another 10 minutes before shutting off. LVP was measured at 3V for each cell.

Next for my runtimes I tried with some older Eneloops (4000mAh Total). Simply put the output here is extremely stable for the entire runtime, and the light ran until 2 hours and 20 minutes of output. The last test I did was with some Amazon Basics High Capacity Ni-Mh batteries. These are said to be rebranded Eneloop Pros but at about ½ the cost. Mine averaged 2475mAh each after testing the cells independently. Overall runtime here was 3 hours and 4 minutes. The extra roughly 800mAh buys you about 45 minutes of extra very stable runtime. Heat on either Ni-Mh was basically ambient temps.

While the light does run on the three different chemistries of batteries, it’s my opinion that the best option is really lithium ion 14500s as these give the most output and still a good amount of runtime for an EDC style light of this size. Alkalines should be the battery of last resort due to their lower output and potential for leaking; it would be a shame to damage the light from preventable corrosion. Since the batteries are in parallel the light will run with only one battery if you wanted. Same outputs, but just less runtime. It can be a weight savings measure or if there was only one cell left in the package in an urgent situation.

The driver has one odd quirk that you should be aware of if you run the light until low voltage protection kicks in. If it takes longer than 30 seconds to change the batteries there is a good chance the light won’t turn back on with fresh cells. The solution is to just leave the tail piece off for 2 minutes to reset the driver. The technical reason for this is there are two sets of code for each voltage range the driver operates on. This could have been eliminated but it would have increased the driver’s parasitic drain, which no one wants. 



The Synergy 2 is using its own UI system, but don’t let that be a worry. It’s simple and familiar. It’s a simple ramping UI. From off, a long press of the button will give you a shortcut to the lowest mode of output. From here a long press again will start the light ramping up in brightness which takes about 2 seconds to reach the top output. Unlike other flashlights there is no flash to let you know you’re at the top or bottom of the range, but this isn’t an issue as the light just stops and doesn’t cycle over. While ramping you can stop anywhere and press the button again to reverse your direction of the ramp. Double press from on or off to jump to maximum output. There are no blinking modes on the Synergy 2, and I don’t miss them personally. 



  • Great emitter choice, nice tint and high CRI
  • Multi Chemistry battery support (Alkaline/NiMH & Liion)
  • Impeccable Fit and Finish
  • Made in the USA!
  • Lots of color options but they are not always all available or published.



  • No moonlight mode, lowest mode of operation is approximately 2 lumens with Ni-MH batteries and 5 lumens with 14500s.
  • The light is a little picky about the length and diameter of 14500s
  • The side-by-side format takes up a decent amount of pocket real estate. 



The Frelux Synergy 2 is a unique light in the flashlight market. It’s a custom light in the sense that it’s made by one man in his garage in the USA, to exacting standards. Everything about it but the LED and eSwitch are custom designed for this light and made in the USA. Ben machines the light himself, anodizes them inhouse in a variety of colors, solders the USA made circuit boards, and does final assembly and testing himself (and sometimes with the help of the kids). The result is a light that has very tight quality control and superb attention to detail. 


It has creative design features too, like you can mix and match body pieces with other Synergy 2’s to create your own color and button combinations. The door is open to different materials for the body sections and buttons too, if he chooses to make this not only a custom light but a highly customizable one too. 


The adjustable tension clip is a smart design that I find works pretty well, and being deep carry I find it’s retention is good tool. It stays in place too during battery changes, which is an upgrade over the Synergy 1. This isn’t all the clip does though; it can also be used to tighten the brass nut that keeps the center section mounted to the head too. 

The Synergy 2 does all this at a price that’s less than your typical custom light that’s made in the USA. It’s a light I have thoroughly enjoyed watching develop on the Frelux Instagram  account, and mine will definitely be in my EDC rotation. I imagine I will carry it more when I am wearing jeans vs shorts due to its width, but that’s largely a personal preference with how I carry a knife and smartphone too.

These are truly custom made lights at this point, with Frelux taking preorders and then producing lights in batches and finishing them to your color specifications. So if you are interested in one, be prepared for a potential wait. Wait times so far have been fairly reasonable in my experience, with Frelux being careful about how many preorders they take. So if you want one, make sure to join the Frelux Facebook page and follow them on Instagram too so you know when preorders open.

Overall this is a fun light and one you should definitely check out if you want to get something unique, custom designed, and made in the USA.

Frelux Synergy 2 Order Page:
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Frelux Synergy 1 Review (Custom EDC Light)

The light I have here is the FreLux Synergy1 pass around light, that has been going to various forum members to play with and review if that is what they do. This is the first review I am aware of that features the updated driver, with the high CRI Nichia emitter. It’s brighter than the previous and has better mode spacing. I didn’t buy it and by the time you have seen this review it will be sent on to the next lucky pass around member. Thanks to Benjamin and /u/ozythemandias for letting more people try this new little light.

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The Synergy 1 comes in a small Altoids sized tin. There is laser cut foam that fits the light perfectly. Inside is a sticker showing battery orientation. On the outside the Frelux logo is laser engraved into the tin. There isn’t a manual with this light, but it really doesn’t need one. I would like to see a certificate of authenticity or serial number card included, it’s pretty common in the custom knife and flashlight market.

Benjamin is an instamachineist and owns his own IT services company. His level of detail and tolerances in the parts are first rate. You can just tell that a lot of time and thought went into the design of the Synergy 1. For instance batteries don’t rattle even with the cap off because the tolerances are so tight. They just kind of glide into place. All the edges are nicely chamfered and more. All the aluminium parts are manufactured using a Fanuc RoboDrill in Benjamin’s garage in the USA.

My version here is a tumbled aluminium that’s been clear anodized. Tumbling is super consistent. Even the pocket clip is tumbled, which I like because it helps hide any scratches. The light also came with a small wring where you could attach a lanyard if you wanted.

The shape of this light is different and hard to describe without seeing it. It’s a side by side battery configuration and a little bigger then a bic lighter. The end profile of the light is almost a figure 8, with the outsides being a bit wider, than the middle. The top, has some machined jimping, almost like a picatinny rail, but much closer together and not as sharp but enough to lock in for grip. This top is a hexagon shape, with angular sides, corners are rounded over. This taller area is where the emitter is and it’s sticks out the most. The bottom area is rounded over and just has small flat on the bottom with a small area of jimping where your index finger naturally sits. When you hold it like this, your finger naturally fits over the single switch.

The rear is a separate piece, it has a single central thumb nut that keeps things together. It’s cut like a gear but with the teeth being shallow and having flats. This keeps the light together and the clip in place. The nut threads onto a small threaded brass shaft that keeps all 3 main body pieces of the light together.The tail cap itself has markings engraved on it to “Reload” and “Make Ready” to loosen, and tighten the tail cap. The edges here are machined and nicely rounded over allowing you to get a good grip and pull the cap onto the light, and tighten the nut with the other hand.

This is an older or prototype body I believe because it doesn’t feature the positive and negative symbols on the body itself. This is a nice improvement and one that basically solves the problem of knowing which way to install the batteries. I think a keyed approach would also work well.

The light is using a Nichia 219C high CRI LED, in a fairly warm tint. It’s using a double anti reflective coated lens, underneath is a small short reflector that has a mild orange peel.

The beam pattern is nice for EDC in my opinion, it’s similar to a TIR style optic but with a hotter center, and dimmer spill. For me this is great for EDC, it’s enough light to see a bit of distance but also wide enough to see around you too. For me I tend to use this type of light under desks at work, looking in the mailbox, quick walks with a dog, etc

The Synergy 1 has very recently received an updated driver that improves the UI and outputs. The new Nichia driver has the following outputs at 30 second intervals: Low 1.4 lumens, Medium 25 lumens, High 125 lumens.

High Runtime
For my runtime tests I used 2x Amazonbasics NiMH rechargeable batteries. High was a very consistent output for 55 minutes before a rapid decline the last 5 minutes. Total runtime was 61 minutes before the light turned off. This was pretty respectable for a light outputting 125 lumens.

Medium Runtime
Medium was more of what I would expect to see from an NiMH typical S discharge curve. Total runtime was about 525 minutes or 8.5 hours. Most of this was at about 65% relative output, decreases were small and smooth.

Low Runtime
Low is only 1.4 lumens so it lasted a very long time. It’s the longest runtime I have actually tested with Ceiling Bounce. Just shy of 3000 minutes, or 50 hours. The graph has one spike that I have to think is an error. The last 500 minutes or so did see a step down before the light decreased.

UI is very simple on this light, Low, Medium, and High in that order. One thing I have noticed with the updated driver is that on low, I sometimes get a very brief flash when I first turn the light on. I think this is because

How does it carry
The Synergy 1’s design is well thought out. I carry it in a right small jeans coin pocket and tend to hold it in my left hand in kind of a pistol type grip. My Index finger perfectly aligns with the milled jimping on the bottom and my thumb fits nicely on the jimping on top. This leaves my pointer finger easy to access the button to function the light.

In the small coin pocket it fits nicely, but you do notice the thickness a bit. I usually have a knife in my right front pocket, and a few other random things deeper down. Ever since surgery my phone lives in my left pocket and when carrying this light I prefer it that way. If I put my phone in the right pocket the chance to scrape or scratch the screen as I draw my phone increases which I don’t care for. Other then that it carries nicely here. For me it’s comfortable to sit in an office chair with the light in this pocket and my seatbelt doesn’t interfere in the the car. I have carried it a little in the left front pocket and don’t care for it as well there due to it being a tad wide to share the space with my phone.

*Pro’s *

  • Made in the USA with fantastic machining and tolerances. I would love to see a Made in USA (Or Flag) somewhere on it, maybe inside the tail screw recessed area.
  • While my version is clear anodized I have heard only fantastic things about the colors being offered. If I end up getting one it will definitely have some color.
  • I like how upgrades are available such as anodizing and a titanium pocket clip.


  • The switch is mechanical, it takes a good amount of force to use and is loud. I also seem to get a brighter flash before getting low sometimes.
  • Battery polarity markings, My older body doesn’t have the + and – markings that newer lights have, this would help making sure you have the orientation correct. A keyed approach would also be a good solution here.

The Frelux Synergy 1 is a fun little custom EDC light from a maker who wasn’t into the flashlight scene like many of us are. A ton of thought has gone into the ergonomics to make a unique light that feels good in the hand and pocket, while being very functional at the same time. The fit, finish and machining quality are all top notch and easily beats production lights. Version 2 of the driver only improves this light, by offering more output and a revised UI that while very simple is more enthusiast friendly, by being linear and having a true moonlight mode.

If you don’t follow Frelux on Instagram I would strongly encourage you to do so. Benjamin does a great job of posting nearly every day showing what he is working on, new products, build progress, and pre sale notification. This light is being built in batches and so far it’s been super popular, so if you want one you may have to watch closely so that you can get in when a batch drops.

Frelux has recently launched a second flashlight product the FML takes some of the Synergy 1 ideas but instead of being an EDC it’s a worklight with a magnetic base, and the light being on a flexible arm, and scaled up to run on 1X AA for an increase in runtime.

Frelux is definitely a brand to keep an eye on. His designs and ideas in the flashlight game are only getting better. I wouldn’t be surprised to see if Frelux becomes the next Grimsmo type company, growing from a garage to a shop to hiring more than one employee, and upgrading machines to produce more new designs all while documenting and sharing the process on social media. Definitely keep an eye on this company and pick up one of his designs if you into custom lights.