TCSPC accumulates a histogram of detected photon delays relative to repeated excitation pulses. Each cycle supplies a timing reference; many cycles provide the decay distribution. The fluorescence instrument response broadens that distribution. In conventional first-event acquisition, losing later photons in a cycle preferentially preserves early arrivals: this pile-up can falsely shorten the inferred fluorescence lifetime. Keep detection probability per cycle low and check stability when the illumination is attenuated.[ref]