The tail of a flash lamp limits which delayed-fluorescence kinetics can be measured

Rate constants and activation energies of reverse intersystem crossing, used to rank thermally activated delayed fluorescence (TADF) emitters, are often extracted from decays excited by xenon flash lamps. We show that the temporal tail of the excitation, not its nominal width, decides which kinetics such measurements can resolve. In three deep-blue host materials, the dominant "fast delayed" component lies inside the excitation window and follows the excitation profile. Passed through reconstructed excitation profiles, 86 reported literature lifetimes used as simulation inputs show that standard tail fits err by more than a factor of two in 41% of cases for a microsecond-tailed lamp, against 6% for a clean 2-µs pulse, and that activation energies are compressed. Reconvolution with the generating profile largely removes the simulated bias; a measurability map identifies conditions requiring an independently recorded excitation profile.