Absorption is the underlying reason for the change in luminescence traits. And the lifetime influences the absorption in turn. This is a common law not only suitable for photoluminescence but also for other types of luminescence. In field emission display, two kinds of luminescence center have dramatically dissimilar lifetimes, which are co-doped in the same material. The spectrum changes with excitation frequency. Tuning color comes into reality in the same materials. The experiment proves that this law has something to do with lifetime, but has nothing to do with the way of excitation and the reasons for abruptly quenching.