I feel like the D4K is what the D4 was always meant to be.
Plus, I’ve arbitrarily decided in my head-canon that “D4K” has the same naming convention as “i18n”… which means “i + 18 letters + n” or “internationalization” (i.e. supporting multiple languages).
But in this case, it’s “d + 4 letters + k” or … “defork”. To remove fork(s). 
Thanks for reviewing!
If I have the light sitting on my nightstand at night I can see the light coming from the aux LED’s on the ceiling.
Right?? Isn’t it awesome? What good is a disco mode if the lights couldn’t project on the ceiling? I wish they were even brighter so I wouldn’t need to set up so many flashlights at my raves.
For real though I do think the aux lights should be bright on high. As bright as you can make them. It’s high mode afterall. If it’s something you wanted to leave on 24/7 you would use low mode. High mode is for showing off your cool aux lights.
I think the low setting should be brighter too. That actually would solve the issue. You probably only go into high mode because the low isn’t bright enough? A brighter low mode would be the same result as making the high mode lower. Then you’d have a low mode that’s more practical for locating your light and you still have a high mode for dancing. Everybody wins. Except the guys that want a really dim low mode I guess. I find it too low to have any use personally. On all lights.
It’s not great that it dented a p42a. Thats one of the few 21700s that’s actually 70mm long. Most go over that. Lishen’s are usually 71-72mm. Hopefully that’s not typical of the d4k
Nice review!
I just received mine this week, d4k dual with w2 green / w1 amber.
It has an amazing flood, like my sbt90.2 with less throw of course… i disabled all RBG leds to be honest, bit annoying when walking with the dog in the dark! One thing I directly noticed is the immense of heat that the light generates on single and both channels on! Even on 120 it will be unsustainable to hold due the heat after a minute. I didn’t changed the temp limit and it’s set to 45c.
Never the less… my ts30s and Acebeam l18 will collect dust I’m afraid…
The aux LEDs are mostly there to replace tritium vials with something more practical. On low mode, they glow a bit brighter than tritium, and are not meant to illuminate other objects… only to help locate the light in the dark and show the lockout state and approximate charge level at a glance. They’re meant to be on all the time while the light isn’t in use, without significantly affecting battery life… so the power draw is generally 0.1 mA or less. This gives years worth of standby time.
The brightness of low mode is determined entirely by Atmel. This mode works only because the Atmel MCU has an internal resistor, which Anduril kind of abuses for a purpose it wasn’t designed for… to reduce the power flowing to aux LEDs. The difference between high mode and low mode is whether the MCU’s internal resistor is enabled.
High mode’s brightness is determined by the resistors on the aux LED board. Usually they’re balanced to make the colors look similar in brightness while using high mode. The intended power draw for those is roughly 0.3 mA to 1.0 mA, to give a brighter level which is still practical… but most manufacturers set it much higher instead, to make it look more impressive at the expense of practical utility. Some even go up to 15 mA or 20 mA.
With the resistors shorted out, it can go up to about 40 mA or 45 mA total, which is the maximum amount the MCU can supply. But that’s not very practical, since it would drain a battery in just 2 or 3 days… and Atmel recommends against this because it can damage the MCU over time. Additionally, the aux LED beam is almost always full of artifacts, not intended at all to be shined at things.
I generally find low mode is bright enough to see during the day, though I may have to put the torch in a shadow if there’s something shining at it. At night, it’s bright enough to see from dozens of meters away, and if it’s on my nightstand or something, I aim it away from me because otherwise it’s bright enough to see light through my eyelids. In blue and/or green mode, even at just 0.08 mA power draw, it’s enough to let me see things 1m to 2m away at night.
For a bright disco mode, you would need RGB primary LEDs instead of aux LEDs. This would dramatically increase the amount of power they can use, while also giving them a proper beam shape and the ability to use PWM for smooth color and brightness adjustments. You could, for example, make a 3-channel light with 4 LEDs… 2 red, 1 green, 1 blue. Then run my lightsaber firmware on it to generate a bunch of interesting user-configurable color patterns.
I hope to include that sort of feature in Anduril eventually, and might even add it soon since I’m doing multi-channel stuff at the moment. But I don’t have a suitable RGB light to test it on.
@ToyKeeper Isn’t there a branch of Anduril that lets you control the button aux seperately form the main aux? I like high aux mainly because I can’t see my chosen button light color otherwise. I would choose low main aux and high button aux if it were possible.
Yeah, someone published a branch with that feature. I’m debating adding it to trunk. People could use 8C or maybe 8H to desync the two sets of LEDs. However, it would probably only be on devices with MCUs bigger than 8K, since there’s basically no room left on older devices.
Primary RGB sounds amazing.
Older devices meaning things like the original D4 series, or would this also exclude current gen D4V2 FET+ drivers?
Yes, anything with attiny85. Original D4, for example. Or Convoy’s brand new Anduril driver. I’m not sure why he went with t85 instead of something newer… I haven’t been involved in that at all.
My lightsaber driver used t85, but it only did lightsaber stuff. It didn’t try to fit Anduril plus all the colorful modes, so it actually has quite a bit of space left.
I understand. But it’s awesome when they are bright enough to illuminate other objects. You can use Red at night if you’re just looking through a drawer for something. Bonus feature
For finding it in the dark and stuff like that I use the blinking mode. Thats a good in between. The low mode doesn’t really help me find it in the dark. It would help me find it if I knew approximately where it was. But if I actually can’t find it, it’s somewhere the lows wouldn’t help with. It’s underneath something. But disco mode on high it’s not gonna go missing.
But that’s the way I use them. And I unscrew the tailcap a or take the battery out always if I’m not actively using it or going to use it in the next hour. So having a low drain aux isn’t a priority for me. Just me personally. I understand why some people would want it low. Still think the low is too low tho. But definitely can see people complaining when the battery is dead after they left the aux on for a year because people would do that. If you’re not going to use the light for a year what are doing leaving the aux on lol. Take the battery out. That’s too long.
I can imagine the response to that would be:
“But I have to have it ready for an emergency”
Idk, im not even gonna leave ammo in a spare magazine for 6 months straight without checking on them never mine loaded. Stuff can corrode.
From the review:
Domed 519A’s work really well with the 10621 optic. They produce a wide and fairly well-defined hotspot that I find very pleasant to use. There are a few minor artifacts here and there that you may notice when white-wall-hunting but overall it’s a delightful beam shape and I highly recommend this combination. I just love the crisp circle hotspot.
That “crisp circle hotspot” really is fantastic. I generally like to use the 10621 over the 10622 for the extra throw, but I also just think the 10621 beam looks nicer with many/most LEDs.
Also always good to see your regulation graphs! I know they take a lot of work to do so I really appreciate that. Still, other reviewers should do this! At least for turbo/high it would be really helpful to see on a lot of lights. Runtime graphs don’t give the full picture of regulation. At least for me it’s REALLY helpful to know how close to max output a light can achieve on a lower battery.
And it’s good to know for people considering a D4 or other quad hanklight - as in the data from your D4SV2 review, the linear+FET driver still achieves much higher brightness at almost all battery levels than the boost driver. The boost advantage is in sustaining ~1000 lumens for ~15 minutes vs the FET dropping over only a couple minutes, and sustaining ~500lm vs the linear+FET ~250lm over the long term.
But 250lm vs 500lm isn’t a massive difference in perceived brightness, so I think for a lot of people who aren’t ceiling bouncing for an hour+ or who don’t really need more than a couple minutes at that higher level, the linear+FET makes a good case for itself in EDC and general use, and especially outside where a short period of very high brightness and more throw can be very handy ( ~219m with linear+FET vs ~160m with the boost is a noticeable, useful difference, even if the FET drops over time) , and you also aren’t likely to need more than ~250 sustained lumens for walking around.
Of course for a EDC that’s used more often as a work light, where you’re lighting up an area indoors at close range, the extra 250 sustained lumens can be nice to have. The ~20% longer runtime is also an important advantage for the boost driver in many circumstances.
Great review as always.
I recently got a D4K with 10621 optic, and soon replaced it with a 10622. The 621 might work for 519A (dunno, haven’t tried it), but it made 219B look pretty ugly. I also tried it with a W1 emitter, but it seems to be soldered somewhat off-center so it looked bad in both optics.
The 10622 is probably a good default for anyone who doesn’t have specific reasons to get something else. 10621 can be more throwy but is also much more prone to creating beam artifacts. 10623 is by far the smoothest and makes anything look good, but it’s so floody that it takes quite a bit more power to light things up to a practical lux. The 10622 sits between as sort of a Goldilocks optic.
Agreed. I took pictures of 10621 vs 10622 for 219b 4500k and E21a 4500k to show the effects.
I prefer to have more throw in these small lights, but have found more throwy optics lead to more artifact/tint shift.
The same pattern is seen in Convoy S21D.
For my kind of use (lots of lower level illumination) I prefer the boost driver because of its efficiency. Much less energy burned as heat by the driver, longer runtimes.