So, I've got a bit of a conundrum at hand. (THE CURSED BUILD CONTINUES)
That was a 1.5ohm, 2W SMD power resistor, connected to the red LED on my tri-cree from a Proffie 2.2. According to three separate LED resistor calculators and my own math (R=(Vs-Vf)/I, so (4.2-2.95)/1: 1.25 ohms, and P=(Vs-Vf)xI, so (4.2-2.95)x1: 1.25W), that was the correct resistance and power for a red tri-cree with a forward voltage of 2.95V at 1A (measured with a power supply, not just read off the data sheet.) In fact, most recommended a 1.5W resistor, but I couldn't find one in a 2010/5025 package, so I bumped it up to 2W which was available.
And it overheated and blew in about 30 seconds. I'm trying to work out why, and how to fix it.
I replaced that array with a second one, and while that didn't explode, the red resistor did overheat rapidly. 0-95C in ten seconds. I replaced it with a non SMD metal film resistor, which took a little longer (90 seconds, approx, not surprising given the extra mass of a full size resistor) to heat up, but it got to 80C.
if anyone's got any ideas, I'm all ears.