I built a 4096-pixel LED array (64x64 addressable pixels) that, when lit fully up used something like a kilowatt. However it was about 4 feet by 4 feet with sp

I built a 4096-pixel LED array (64x64 addressable pixels) that, when lit fully up used something like a kilowatt. However it was about 4 feet by 4 feet with spacing between each pixel and could run just fine without overheating. These days I'm working on a PCB with many LEDs on it and heat management is much more challenging; I ended up designing the board so that the LEDs sit on thermal rectangles with through-holes (vias) that connect it to a massive ground plane (in this case it's "thermal ground" not just electric ground), as described in the datasheet for my LED chip. Each LED is 3W so it can get hot really quickly, but as long as the board is adequately coupled to a larger heat sink, it can run at fairly high power. Thermal coupling is harder than I expected! I have learned you can melt solder with a hot LED(!). Also, it helps to run LEDs at a lower-than-max power; you get most of the light but less of the heat. Keeping LEDs in their happy zone prolongs their life signficantly.