Astrolux S43

The Product

This is the Astrolux S43, a high powered quad-emitter light, and the first product sent to me from them. The light has a side switch, built in micro-USB charging, and a ramping UI. The included cell tubes mean the light can run on either an 18650 or an 18350 cell.
Astrolux has a good history making quad-emitter lights. First was the S41, a tail switch quad made from aluminum, and it’s matching S41S, which was a version made of stainless steel with a copper heat sink. This was followed by the side switch S42, which made the move to a side switch and added built in charging, but had a rather divisive UI. The S42S with the same stainless steel and copper was produced as well. Now, we have the S43, in aluminum, and the S43S, in aluminum with a copper heatsink. The unit I’m taking a look at is the S43, with four Nichia 219C emitters loaded into the front - it’s also available with higher output XP-G3 emitters, at the cost of beam tint and CRI.


This light manages huge output out of a single cell, and the light it makes it as great as you can expect from the 219C. I carried it a bit less than I expected to, mainly because I prefer lights this size to have a bit more reach, and I don’t like the idea of burning a hole in my pocket - but if you’re looking for huge pocketable output, you should definitely look at this one.

Physical Dimensions

The light measures 30.5 mm across at the widest point, just above the switch, and 19.9 mm in diameter along the body tube. With the 18650 tube, it measures 122.2 mm long and weights in at 89 g without a cell. Swapping in the 18350 cell tube brings the length down to 89.2 mm, and the weight to 74 g.


The head of this light is the most interesting part - there are 4 Nichia 219C emitters shining into a quad optic. The plastic optic is covered with a glass window, and held in place with a slightly crenelated bezel. I would prefer a smoother bezel, as this one sticks out a bit further than necessary from the lens, but that’s a matter of personal preference. This is also something I’m sure to mention a few times - I have a liking of compact lights, and there are a few spots where this light seems to have added a bit more metal than I feel is needed. The bezel also has the brand and model etched into the anodizing.

Behind the bezel, one side of the light has the switch. Astrolux was thoughtful about the design here, and they did a great job. The rubber cover on the switch is domed, which makes it easy to find by touch. It’s held in place with a bronze colored metal ring. The area around the switch is milled out into the body of the light, so the switch itself is set in and difficult to press accidentally. There are red and green indicating LEDs behind the switch cover. This section of the light also has some fins cut into it to help with cooling.

Opposite the switch, a silicone cover keeps dust and debris out of the micro-USB port used for charging. The port cover seats into the port well enough, but the small toggle used to help remove it is easy to flip accidentally with a finger while using the light. I would not recommend submerging this light if it can be avoided.
The body tube, whether the 18650 or 18350 is used, is smooth without any knurling or other decoration. There are grooves for the clip at both ends.
The tailcap is knurled, which is good for grip, and it has a lanyard hole as well. The tail is flat and can balance the light. The large hole in the light is for the tripod thread or spike, which are included with the light. I would rather these accessories were left out and the light shortened, as I don’t see either of them being particularly useful.

Inside the tailcap, the threads are square cut and anodized. Mechanical lockout is possible with a small twist. There are two nested gold-colored springs that serve as the negative contact for the light.

Inside the head of the light, the driver appears to be pressed into place. There is no spring at this end of the light - just the bare PCB for the positive contact. My light had frequent issues losing contact with unprotected flat top 18650 cells. I’m not sure if the cause of this is the bare positive contact, the length, or a poor connection, but it was noticeable and unfortunate. Button top cells would probably resolve this issue, but so would including a positive spring.

What’s Included

This light comes with a thorough kit.
  • Astrolux S43 (with the 18650 tube) 
  • Lanyard 
  • Friction-fit pocket clip 
  • 18350 cell tube 
  • Tripod thread adapter sleeve 
  • Stainless steel spike 
  • O-rings 
  • Paperwork 

Ergonomics and Retention (and spikes)

This light feels good in the hand. The knurled sections of the tailcap make it slightly larger than the body, which along with the bigger head make sure it stays firmly in hand despite the smooth body. There's a hole cut into the tailcap to attach the included lanyard.

The pocket clip fits at a groove at either end of either of the included cell tubes. The clip loops back for a great deep carry, and won’t leave much of the light above a pocket at all. My one complaint with this clip is that it sticks out quite far from the body of the light at the point where it attaches. That usually catches on my pocket, and means I need to carefully thread the fabric into the clip if I want the deep carry.
The tail of this light also has a hole threaded into its base at a size compatible with most tripods. A stainless steel sleeve is included to reduce the size of the hole. The sleeve protrudes slightly from the base of the light, and makes tail standing slightly less stable when installed. It also has a groove cut into it so it can be removed with a flat screwdriver if installed too tightly.
I don’t personally see much utility in tripod threads on the tail of a light like this, and I would prefer a flat tailcap that added less length to the light and perhaps included a magnet, but I’m sure there are users that will appreciate this feature.
The light also includes a steel spike that can be threaded into this tripod attachment. The product page refers to it as a “tactical survival hammer”. I’m sure it would hurt if you hit someone with this, but I’m not about to test that theory.

Modes and Interface

This is certainly one of the major highlights of this light - the light uses NarsilM, which is a firmware that allows huge amounts of customization. You can configure basic things, such as switching from standard modes to ramping user interfaces, all the way up to setting the temperature you want the light to step down at. Narsil is complex enough that I could do a whole write up on it, but I’ll just say that it’s fantastic and I am extremely pleased to see more lights using this and similar interfaces.
I left the light in the stock ramping mode - single press for on or off, hold to ramp, double tap for turbo.

Light Quality and Beam

This light uses 4 Nichia 219C LEDs under an optic. The light is also available with 4 XP-G3 emitters instead, if you would like to give up CRI and color quality for raw output.

Power and Runtime

This light can run off of either an 18350 cell or an 18650 cell - my tests were all performed with an unprotected flat top 30Q. In my experience, small bumps were able to break connection with the flat top cell, so a button top may work better.
The driver used in this light is a direct drive setup, which means a lot of things. First of all, almost any protected cell used in this light will not work properly - the current draw is high enough that unprotected cells are highly recommended. Secondly, this kind of driver means that testing performance is very touchy. A FET or direct drive light basically just straps the jumper cables from the batteries to the LEDs in turbo mode and hopes for the best. The good part of this is that you really get the highest possible output from the light, but the downside is that any slight change in temperature, cell, how clean the contacts are, or any other number of factors will drastically change the results.
My runtime tests have been shortened here to show two separate starts at two different temperatures. In both cases, the light starts way up around 300% of the output once the light has been on for 30 seconds. During this time it gets extremely hot to the touch. Also in both tests, the light settles at about 15% of the output at 30 seconds, and stays there for the rest of the test. Notably, the light does not try to ramp back up after cooling down.


Charging of this light was measured at about 0.75 A at the USB port for the constant current phase of the charging. After 2.5 hours, the constant voltage portion of the charge starts. There’s a solid drop off when the charge current has dropped below 0.1 A to prevent the cell from trickle charging. Overall charge time was about 5 hours for this 3000mAh cell.
When the light is charging, the LED under the switch glows red. When charging is complete, it switches to green.

What about the D4?

I feel it would be unfair to finish up this review without mentioning the Emisar D4. The D4 has been out for a bit longer, and these two lights have a lot in common:
  • Available with 4 Nichia 219C emitters 
  • Made of aluminum with other metals optional 
  • Available to run 18650 or 18350 cells 
  • Side switch running a ramping firmware 
  • Direct drive setup for maximum output 
  • Lots of heat and fast step downs 
So what sets these two lights apart, and which of the two should you get? The Emisar is certainly a much more compact light - for me, that’s a big draw. The S43 has a lot of extra length in the cell tube and that tail cap. That being said, the D4 made a few compromises to get so short. One of the largest is that it can be very picky about the length of cells it supports, whereas the light being reviewed here today has plenty of room in the tube (maybe too much).
The goal to get the D4 as small as possible also means it loses out on a lot of extra features. Here’s what the S43 can do that the D4 can’t:
  • Integrated charging 
  • Backlit switch 
  • Lanyard loop 
  • Tripod hole 
So which is better? That’s tough to say. In the end, it depends on what feature set is more important to you. It’s also worth noting that the D4 has more options for emitters, optics, and body color.
Personally, I can do without the integrated charging and would lean towards the D4, but I have seen countless posts where people have asked for exactly this feature. I think the S43 could be improved with a shorter tailcap that had a magnet instead of a tripod thread, as both these popular lights are missing that feature.



  • Huge, high CRI output 
  • Backlit switch 
  • Great ramping UI 
  • Solid built in charging 


  • Step downs are quick and drastic 
  • The light puts out too much heat for turbo to be usable for more than a few seconds 
  • Light is too long for my liking and for my cells