The purpose of this Application Note is to provide information for rapid temperature cycling of a thermal load over wide temperature extremes using an ILX Lightwave LDT-5980 120W temperature controller. The focus will be on controlling a 1.5W thermal load at temperatures of 0°C, 25°C and 85°C. Because optimizing the LDT-5980’s PID control loop can be a time-consuming task, even with the instrument’s Auto-Tune feature, examples of PID constants will be provided that allow the LDT-5980 to rapidly change and stabilize the thermal load’s temperature.