I suspect that only a negligible proportion of the heat is shed via radiation: if I get a light really hot, hold it with horizontal orientation, and put my lips (which are very temp-sensitive) right below the heatsink area (without touching it), all the heat my lips would receive would be radiation, which I cannot feel at all. But if I position my lips above the light, I can feel the hot air rising, and if I were to touch the surface, it would feel very hot, indicating that both conduction and convection (which in this case is just conduction to air) occur at much faster rates.
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Agreed. I think that in these small lights radiation is just not fast enough, no matter what the material is. I have 3 D4V2’s in 3 different materials: aluminum, copper, and brass. I could test but unfortunately they have different LEDs. It seems they all step-down equally fast.
A fan blowing on the lights otoh makes a huge difference.
Replying also to be the 1000th post in this thread. But QR beat me to it. 
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I’ve had a few 519a lights, some domed (Wurkkos TS32), some dedomed accidentally LOL (S21D), some tint mixed (S21F), but bought this last one, a red Hank D4K, because I saw it on Toykeeper’s Favorite Lights list.
I’ve had it for a while now but have been too busy with the Fireflies to measure it and take beamshots. I wish that there were on-board USB-C charging but otherwise, from beautiful 519a 5700k dedomed tint, to easy of handling and quality, to sustained brightness (if a little hot), this light is a home run. I recommend it extremely highly, in particular the version with the Lume X1 Boost driver. It costs some extra $12 but is well worth it.
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It is interesting you say rosy looks beautiful because it resembles a natural phenomenon, when green tints resemble an even more beautiful natural phenomenon called the aurora.
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Last night, I took out the Hank D4K, and two formidable competitors, Convoy M21B w/ Nichia B35AM 4500k and Firefly E07X w/ FFL351A 4000k Rosy, for my evening walk. I consider real life use the final arbitrator of a light’s worth, nearly regardless of specs. From the standpoint of tint, for my taste, these 3 lights are THE giants in my small light collection. They are for me, together with the reference stadard 219b 4500k in Convoy S21D, the “best” of all the lights that I’ve cherry picked based solely on great color rendering.
And the WINNER is… none. I could not pick one LOL. It’s remarkable that 3 lights with such different specs and designs could be loved equally. 
Not too surprising perhaps, they ARE my top lights.
Hank-Emisar D4K w/ 519a 5700k DD:
Driver: Lume X1 (this is the $12 Boost option on the Hank website)
Output: 2000 lm
Throw ANSI (30 sec): 218 m (longest throw among my quad Nichia lights)
CCT: 4100k
Fireflylite E07X with FFL351A 4000k:
Driver: Lume 1
Output: 4330 lm
Throw: 269m
CCT: 3900k
Convoy M21B with Nichia B35AM 4500k
Output: 1090 lm
Throw: 263m
CCT: 4300k
Heat: Of the 3 lights, the Hank D4K runs hottest, to the point of being somewhat uncomfortably hot at the head (default stepdown temp = 50C) . The Convoy M21B is the champ ehen it comes to heat management. It runs completely cool as if it’s just cruising at Turbo level. Lastly, the Firefly E07X runs warm, does not feel excessively hot, and regulates its output around default setting 50C as expected.
Output: In my evening walks, I mostly use max ramp level (Turbo minus 1), so although the 4330 lumen of the Firefly E07X is extremely fun and could be helpful temporarily in certain safety situations, it doesn’t come into play as much in practical use.
What really matters is sustained output, and here is where the field is equalized. This is why the M21B with B35AM not only could compete with “only” 1090 lm Turbo output, but also does so extremely well. This Convoy is a “humble” 30 buck light, but I simply cannot recommend it highly enough at this website HERE, particularly because of the tint and color rendition of the B35AM 4500k LED. If you get it, see if Simon has one with the beautiful MAO finish. And ask for green reflection AR lens before purchase. 
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Lume X1 Boost Driver by @loneoceans: I feel this very highly praised driver is a no brainer option for my D4K. As noted by Hank, the boost driver output is limited in comparison to the default driver (only at Turbo level, which AFAIK is FET), but it is more efficient (90-95%) with a longer running time and less heat. Really, in this small light a FET turbo would only bring heat and super-quick stepdown. If anyone needs a “lumen fix” , there are those ridiculours Nightwatches. Tiny D4K is not the place. loneocean’s discussion on this driver here: << Lume X1: 40W Single-Cell Boost Driver with Anduril2 and UDR >>
Default Stepdown Temperature and Calibration with Lume drivers: I asked Hank and was told that with the Lume X1 Boost driver, the default Tmax is 50°C and there is no need to calibrate. My Firefly T9R with Lume1 Buck+FET Turbo driver similarly has Tmax at 50°C (perhaps this 50°C is default-standard for Lume?). Upon further googling, it appears with these drivers the temperature is factory-calibrated (and so is voltage AFAIK), and that’s why calibration is not necessary. Anyone pls correct as needed.
D4K notes:
Green reflection AR lens: I have four Hank D4V2’s that were bought a couple years ago. 3 of these came with non-AR lens, and the 4th one has purple-reflection AR lens. The D4K is the first time I got green-reflection AR lens in my Hank lights. If you are to order this fantastic light, I would probably check with Hank to maker sure you’ll receive the same green-reflection lens.
Comparison of knurling, color, and finish of host:
Vs D4K, the knurling of Firefly E07X is quite a bit deeper and make the light more grippy to hold. Cosmetically, if you like that deep knurling look, Firefly’s is most beautiful among the lights I have.
Strictly a matter of personal preference: D4K’s finish is more shinny than Firefly and the red, to my eyes, is a slightly touch orangish or maybe pastel, as opposed to a deeply saturated red. I hope the picture shows this. Personally I prefer a more matte finish and the more “deeply” red, for example, of Firefly’s vine red finish.
This observation is so subjective that if you feel differently, there would be no argument from me. Bottom line is I absolutely love the inherent quality of the D4K and would have bought it regardless of what color or how shinny the finish is. I am glad that at least red is available.
