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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