Emisar D4S review

Well, the cat is out of the bag. Emisar has a new light called the D4S.

It’s like an Emisar D4, but sized for a 26650 cell, throwier, and with some other misc improvements. It also has cyan-colored aux LEDs under the optic, 16 of them, which work a bit like tritium vials.

For anyone who is not familiar with the Emisar D4, two things:

  • I did a thorough review you might want to read for context: TK's Emisar D4 review
  • It is a “hot rod” in the hottest sense of the term, and can start fires. It has earned its reputation as a “nut roaster”, so caution is advised. Lock the light while not using it, by clicking 6 times or loosening the tailcap.

The D4S is a more appropriate size for its power level, has some extra protections built in, and should be less prone to starting fires. However, it is still designed for maximum output and caution is still advised.

Disclaimer: I am not an impartial reviewer. I was hired to write the firmware for the D4S, I received a prototype unit for development, and I received a near-production unit for review.

Disclaimer 2: Since the light isn’t actually out yet (as of 2018-07-14), I don’t know a lot of details about official specs or models or anything. I’m reviewing an almost-production unit which shipped without branding or O-rings, but should otherwise be pretty much the same as the final product.

Disclaimer 3: This is a quick and incomplete review since the light showed up only a day before I leave for a trip, but I’ll try to fill in more details over time.

What’s the difference between D4 and D4S?

Compared to the D4, here is a list of improvements… in no particular order:

  • More throw — about 2X-3X as many candelas.
  • Longer runtimes due to 26650 cell.
  • Heats up slower.
  • Higher sustainable output.
  • Higher regulated output: ~400 lm instead of ~150 lm (3x7135 instead of 1x7135).
  • Cyan-colored aux LEDs under the optic.
  • Olight-style square knurling for grip.
  • Lanyard hole in tailcap.
  • Optional magnet in tailcap. Quite strong. Sticks to everything. (I prefer the no-magnet tailcap)
  • Recessed button.
  • Reverse polarity protection fixed.
  • Firmware-update vias added on battery side of the driver, so it can be reflashed without soldering anything.
  • A bunch of firmware improvements, detailed below.

Also, some things which may not be improvements:

  • Larger.
  • Heavier.
  • No clip? (maybe, but it does have clip grooves)
  • Higher price? (TBD)

Auxiliary LEDs

The aux LEDs activate when the main emitters are turned off. On high, they seem about as bright as moon mode but they use less power.

The aux LEDs are only active when the light is off, or locked, and each of these two “off” modes can be configured to operate in four ways:

  • Off
  • Low (~0.03 mA)
  • High (~0.90 mA)
  • Beacon (high for 0.5s, then off for ~3.5s, then repeat) (avg ~0.11 mA)

The aux LEDs on high are bright enough to use as a moon mode, and at under 1mA they have very long runtime. But the beam isn’t the greatest for that sort of thing. It’s an interesting pattern, at least:

Here is how they look from the front:

Or, on the low output mode, they’re close to the brightness of tritium vials. This shows how they’re barely even visible with overhead lights on:

Note: The optic is not cracked. The weird-looking bit at the upper right is where the plastic was injected into the mold, and does not touch any of the optic cups.

Firmware / RampingIOS V3

A lot of things changed in the firmware. I tossed out the old code entirely, and made the new version by adapting Anduril to match Hank’s specifications. So even though it should act mostly the same from a user’s point of view, the new code is totally different under the hood.

Most of the V2 interface still applies:

But there are differences, detailed here. Firmware changes from RampingIOS V2 (Emisar D4, D1, D1S) to RampingIOS V3 (Emisar D4S):

  • Completely new code base, using FSM instead of Narsil.
    • Significantly simpler and easier to modify.
    • Uses dynamic underclocking to extend runtime on the lowest modes. Moon should run about 3X longer per mAh.
    • Can be reflashed with other FSM-based UIs, including Anduril.
  • Supports the use of aux LEDs.
    • To change the aux LED mode for “off”, click 7 times from off.
    • To change the aux LED mode for lockout mode, click 3 times while in lockout.
  • The battery-connection blink is much faster.
  • Lock and unlock blinks are much faster.
  • Ramping stuff:
    • In addition to the smooth ramp, it also has a stepped ramp for those who prefer discrete output levels.
    • Smooth and stepped ramps both have configurable floor and ceiling, and the stepped ramp has a configurable number of steps. This is identical to Anduril, and is configured in the same way.
    • Smooth and stepped ramps can have different settings, which behaves sort of like having two different mode groups.
    • Double-click from off goes to the user-configured ceiling instead of turbo. But turbo is still accessible with a double-click when the light is already on.
    • Holding the button to ramp always goes up unless the button was released less than a second ago. No need to remember ramp direction any more.
    • The user can now “click, release, hold” to ramp down.
  • Thermal stuff:
    • Thermal regulation is much smoother now, too smooth to see by eye, and should be less prone to oscillating.
    • Thermal config is now accessible by 4 clicks from tempcheck mode, in addition to the usual 10 clicks from off.
    • Thermal configuration is completely different now and has two settings:
      • Sensor calibration. Click N times to tell it the current temperature is N degrees C.
      • Set maximum temperature precisely. Click N times to set thermal limit to 30 C plus N. Default is 45 C.
    • TBD: Thermal calibration is done at the factory so the behavior should be more consistent. (?)
  • Momentary/tactical mode uses last-ramped brightness instead of turbo.
  • Momentary/tactical mode stays active until battery is disconnected, so it can be used for signalling. No pattern of clicks will exit the mode.
  • Beacon timing is now configurable.
  • Lockout mode doubles as a momentary moon/low mode, so it doesn’t need to be unlocked for quick tasks.

Update 2018-08-06: Added a diagram for the V3 UI:

For reference, here are the default config values:

  • Smooth ramp floor: 1/150
  • Smooth ramp ceiling: 120/150
  • Stepped ramp floor: 20/150
  • Stepped ramp ceiling: 120/150
  • Stepped ramp steps: 7
  • Beacon mode timing: once every 2 seconds
  • Aux LED mode (off): low
  • Aux LED mode (lockout): blinking
  • Temperature limit: 45 C

Update 2018-08-06: Source code is in my flashlight firmware repository, merged into the trunk (main) branch.

This light is also fully supported by Anduril, for those who want more modes and features. Reflashing is done acupuncture-style with a set of six pins instead of a SOIC8 clip.

Beam / output

The D4S is throwier than the D4, and it has a nice beam with only minimal artifacts. It has a round hotspot, a reflector-like spill area, and then some mild extra junk outside the edge of the spill.


I can’t get great measurements right now, as I don’ have a proper high-amp 26650 cell to use. I’ll have to measure that after I return from my trip. For now, these values are approximate based on some mediocre measurements and sometimes a little math.


  • Lumens: TBD (4000+)
  • Throw: TBD (~45 kcd?) / (~470 m?)
  • Throwiness: 8.8 cd/lm

Nichia 219c:

  • Lumens: TBD (3000+)
  • Throw: TBD
  • Throwiness: TBD

Other emitters? (TBD)

Runtimes: (approximately, using a Shockli 5500mAh 26650 cell) (note: I haven’t measured yet with the correct type of cell, so these values are rough guesses)

  • Aux LEDs, low: ~20 years
  • Aux LEDs, beacon: ~5.6 years
  • Aux LEDs, high: ~8.5 months
  • Moon: ~3.8 months / ~114 days
  • Highest regulated level (~400 lm?): ~5.2 hours
  • Default ceiling (~1700 lm?): ~36 minutes
  • Full turbo, with water cooling: ~13 minutes?

The ramp is shaped to provide a similar amount of brightness resolution at the low end, compared to the D4… but the boundary between regulated and direct drive is higher. So the boundary blink happens later and higher, and it’s closer to the ceiling blink. Above the boundary threshold point, it ramps up pretty quickly.

Beam shots: (whitewall only, sorry)


The D4S body is just what one would expect from Emisar, but with some improvements. Even my early prototype, assembled out of rejected parts, was pretty good. The new knurling is nice, the lanyard hole should satisfy a lot of people who wanted one, the magnet is awesome for people who want one, and the quality is overally very high. The recessed button is also a very nice touch, and should reduce accidental activations, though it’ll be harder to remove the button retaining ring if anyone wants to do that.

The lanyard hole on mine has some sharp edges, but Hank tells me this is fixed in production. Also, my early model doesn’t yet have O-rings or an AR-coated lens, but those are supposed to be fixed too. Emisar’s prior AR coating is a type which doesn’t significantly flavor the beam, so I don’t really mind it. I still prefer plain glass when I can get it though.

The D4S is initially available in green and black. Maybe other colors too (TBD).


  • Length: 104.8 mm
  • Diameter (bezel): 38.9 mm
  • Diameter (widest): 42.3 mm
  • Diameter (tube, knurled): 32.5 mm
  • Diameter (tube, narrowest): 31.0 mm
  • Diameter (tailcap grip): 34.9 mm
  • Maximum battery size: 68+ x 27.5 mm
  • Lens: 36.0 x 2.1 mm

The springs are Hank’s signature springs — extra-low resistance for maximum current, designed to lay flat with a battery inserted.

Threads on the battery tube appear to be trapezoidal, with deep but narrow grooves.

Here’s a size comparison of Emisar’s D1 (in 18350 mode), D4, D4S, and D1S.

The magnet really is quite strong. It grabs onto things with a satisfying thwack and doesn’t want to let go. I had a bit of fun checking out what it would stick to…

Door latch? Check.

Drum throne? Check.

Smaller part of a drum throne? Check.

Wire shelf? Check.

18650 cell? Check.

18650 cell stored inside an aluminum flashlight? Check.

The edge of a single screw attached to a moving fan? Check.

Honestly, I think Hank may have overdone it a bit with the magnet strength. But all you people out there who complained about weaksauce magnets? YOU HAVE BEEN HEARD.


There is a copper MCPCB for the main emitters and a secondary PCB for the aux LEDs, stacked directly on top. The MCPCB is available from Intl-Outdoor.com with various emitters on it.


Instead of a FET+1, this driver is a FET+3. And it has spring-side vias for easier reflashing, because I bugged Hank about it and he liked the idea. I’m hoping he’ll carry a flashing kit too, but I haven’t heard back about that.

Regulated output goes up to about 400 lumens, and full turbo is in the range of 3000 to 5000 lumens depending on emitter type, battery type, and how the measuring equipment is calibrated.

Here is the visible part of the driver:

… and the other side of an earlier revision:

Thermal regulation pattern

Here is the regulation pattern I measured on my D4S prototype with XP-L HI emitters. It shows brightness over time, not temperature.

This was at full power with the light laying sideways on a table with a fan blowing at it. The little bump at the beginning was caused by touching the light to check its temperature. Actual lumen levels are approximate, since this test was done with a cellphone’s light sensor instead of a proper integrating sphere.

Other Emisar lights

In case anyone is confused about what’s what.

The main difference between Emisar lights is the throwiness:

  • 4 cd/lm: D4
  • 8 cd/lm: D4S
  • 33 cd/lm: D1
  • 100 cd/lm: D1S

Also, battery type:

  • 18350: D1, D4
  • 18650: D1, D1S, D4
  • 26650: D4S

And lumens:

  • ~1300 lm: D1, D1S
  • ~4000 lm: D4, D4S

Or overall throw:

  • ~12-20 kcd: D4
  • ~40 kcd: D1
  • ~45 kcd: D4S
  • ~130 kcd: D1S

And of course size and shape.


When will it be available?

  • No idea. Probably very soon?

How much does it cost?

  • I don’t know, but Emisar’s prices are usually very reasonable.

What battery should I use?

  • (TBD) The best one I’ve found is the Shockli 5500 mAh cell.

Why aren’t there more FAQs?

  • um… *eyes dart around nervously* … mistakes were made? … *ahem* … Okay, move along, nothing to see here. Show’s over, folks.

The End

Sorry, I don’t have any branded D4S tailcaps, and showing their bare bottoms might violate the rule against indecent pictures. So I’ll just end things here and wait for production models to cover themselves up.

Wow very COOL! :cowboy_hat_face:

I just bought this quad board and optics a few day’s ago, wonder when Hank is going to be selling the secondary/aux LED top board, and in what colors? :heart_eyes:

Well dang. That’s awesome. Gotta have one.

I been waiting for this one…


You all know I just HAVE to have one of these, right?

TK, excellent work on the cram review, thank you for making it happen. Be careful out there, the best to Queen Goddess. :wink:

Be nice if magnet was removable or had optional non magnet tail cap.

Aux LED’s look awesome!

The magnet is optional.

Fantastic review TK, and certainly another beautiful light that just can’t be ignored,
Every time I decide to slow down on purchasing lights along comes this D4S a must have for sure.
I know, I’ll slow down on my impulse buying of lights, hum does that make any sense…? No…
Have a safe trip TK, thanks again.

I guess by optional I meant be nice to be able to have a removable magnet or a both tail caps available in case it is a permanent fixture of the tail cap.

Any buzz about tube colors?

I don’t know how the retail package will work, but I got two tailcaps with mine.

Nice. Id buy 2. Also noticed that the d4 price dropped 5 bucks and the xpl option also came down in price.

I think I’m in love!

great review

reealy nice flashlight

Ha Ha, I was rereading your review TK and I missed this comment on the first read regarding the D4,

“It has earned its reputation as a “nut roaster”, so caution is advised.” :person_facepalming:



I’m a big fan of flood beam and in my D4 I use the Carclo 10623 instead of 10622 for better flood. The D4S it seems that uses the Ledil Angie-S and for people like me Ledil have Angie-M and Angie-W with more angle of light/flood (and less throw). I don’t know if they are going to be compatible but I think if.


Thanks for the heads up on this new D4S.
Great improvements, especially the UI w floor/ceiling, 26650 format, knurling and aux blue leds.
Love it. Want one. NOW!!! :heart_eyes:

Any ETA?