Fluorescence lifetime refers to the average time a molecule remains in an excited state before emitting a photon and returning to its ground state. This duration is typically in the nanosecond range and can vary based on factors like the environment, temperature, and the specific properties of the fluorescent molecule. Measuring fluorescence lifetime is crucial in various fields, including biochemistry and materials science, as it provides insights into molecular interactions and dynamics. Techniques such as time-correlated single photon counting (TCSPC) are commonly used to accurately determine these lifetimes, enhancing our understanding of complex biological systems and materials.