Quote Originally Posted by sx646522

The best designs will always need passive cooling only - from large heatsinks and well-spaced emitters. Active cooling is merely a bonus after that, not a primary thermal management design priority. Dense modules will always cause entirely too many issues from high junction temperatures (Tj), uneven lighting distribution which mimics old point-source lighting inefficiencies, color shifting, de-rating, and all the rest.
I agree with the passive cooling. I've tried both, and the fan based one made me worry constantly that it would fail. Must be worse in the mass manufactured ones where you can't get at it to clean the dust off so easily.

I don't necessarily agree with your point about emitter spacing. A sufficiently thick copper baseplate on the heatsink will dissipate kilowatts in an area the size of your palm as long as there are enough fins. Aluminium probably isn't conductive enough to do that, but I've had 50w of chips in a square inch without perceptible dimming (side by side with unused module from the same batch) after two seasons.