1500f really isn't fair, as half the heat is contained within the inner arc & outer envelop of the bulb.
Imagine what temps would be on a passive heatsink measuring 10 inches long 3 inches wide(hps bulb) getting 600w of leds fed to it! Lol
You put your Apache at 600 in a sealed 4x4x4 and put a 600w hps in another sealed 4x4x4......if the draw is the same, the AMBIENT room temp will be the same....that's it.
I can't stop!......ha