Fluorescence is the physical phenomenon where a material absorbs light or electromagnetic radiation at a specific wavelength and subsequently emits light of a longer, lower-energy wavelength. This emission occurs when the energy supplied excites electrons within the material to a higher energy state; the subsequent return of these electrons to their ground state involves the release of excess energy as photons. Unlike phosphorescence, which involves delayed light emission, fluorescence is characterized by an immediate re-emission of light upon the cessation of excitation. This property is widely utilized in scientific techniques for visualizing biological structures and chemical compounds, as specific molecules can be labeled with fluorophores that absorb and emit light detectable by specialized instruments.