Fluorescence is a characteristic phenomenon in which solids, liquids, or gases emit light when illuminated. In contrast to phosphorescence, the term fluorescence applies to substances that have no afterglow, i.e. the fluorescence ceases directly upon irradiation of the stimulator. This means that the electrons of the atoms or molecules of the fluorescent substance excited by absorbing the energy of the incident light actually spontaneously return to their basic state while emitting characteristic light. According to Stokes' Law of Fluorescence, the wavelength of light emitted by fluorescence is longer than that of absorbed light:
υe Less than or equal to υa
Ki kote
υ e = frequency of emitted radiation,
υ a = frequency of absorbed radiation.
Fluoresans se limyè ki emèt pa sibstans ki absòbe limyè oswa lòt radyasyon elektwomayetik. Li se yon fòm luminesans. Nan pifò ka yo, limyè ki emèt la gen yon longèdonn ki pi long epi kidonk pi ba enèji foton pase radyasyon absòbe a. Yon egzanp klè nan fliyoresans rive lè radyasyon an absòbe se nan rejyon an iltravyolèt nan spectre an (envizib nan je imen an) ak limyè a emèt se nan rejyon an vizib; sa a bay sibstans la fliyoresan yon koulè inik ki ka sèlman wè lè ekspoze a limyè iltravyolèt rive. Lè sous radyasyon an sispann, materyèl fliyoresan sispann emèt limyè prèske imedyatman, kontrèman ak materyèl fosforesan, ki kontinye emèt limyè apre yon peryòd de tan.