An investigation was done on the effect of fluctuating or rapidly decreasing heating loads on the response of temperature sensitive paint (TSP). An experiment was designed and carried out in the University of Maryland Advanced Propulsion Research Laboratory’s Vitiated Heater with sudden changes in heat flux over time. The results of the experiment showed that the accuracy of the discrete instrumentation under a thin layer of TSP is dependent on the thickness of the paint layer and magnitude of the heating load. It also showed that the accuracy of a TSP measurement with a sudden change in heat flux decreases as the paint thickness or heating magnitude increases when the current data reduction methodology is applied. Finally, a novel dual-calibration data reduction method was utilized to improve the calculated heat transfer accuracy for an experiment with a sudden change in heat flux.