Air temperature readings from a sensor at canopy height miss what is happening on the leaf surface, and sativa leaves run hotter than the air under strong lights because they are so thin. A cheap infrared thermometer pointed at the top leaves gives the number that matters for transpiration and shows when the light is too close well before tacoing starts. The environment section on https://hazesativaseeds.com suggests keeping leaf temperature within a couple of degrees of the air and lists typical readings for LED and HPS. Checking a few spots across the canopy also reveals uneven lighting.
