glow

Glow refers to the emission of visible light by a substance at relatively low temperatures, produced by luminescence rather than heat. It contrasts with incandescence, where light arises from high temperature. Luminescence encompasses several processes including fluorescence, phosphorescence, bioluminescence, and chemiluminescence.

In fluorescence, a substance absorbs light and re-emits it almost immediately at a longer wavelength; the glow disappears when the excitation ceases. Phosphorescence involves trapped excited states that release light more slowly, allowing continued emission after the light source is removed.

Bioluminescence is light produced by living organisms through biochemical reactions, commonly involving luciferin and luciferase, as seen in fireflies and luminous marine species. Chemiluminescence refers to light generated by chemical reactions without substantial heat, as in glow sticks.

Examples of glow in everyday life include glow-in-the-dark materials, safety signs, and various display technologies. In science, fluorescent and phosphorescent tags are used to label biological samples, while bioluminescent systems enable imaging of cellular processes. Light emission is characterized by its spectrum and persistence, factors governed by molecular structure and environment.

The term glow is also used broadly in branding, poetry, and culture to denote warmth or radiance. See also luminescence, fluorescence, phosphorescence, bioluminescence, chemiluminescence.