Certain substances exhibit fluorescence, a phenomenon where they absorb ultraviolet (UV) radiation, also known as black light, and re-emit it as visible light. This emitted light gives the appearance of glowing. Common examples include tonic water, which contains quinine, and many fluorescent dyes used in clothing and posters. The process involves the absorption of short-wavelength, high-energy UV light, followed by the emission of longer-wavelength, lower-energy visible light.
The phenomenon has numerous applications, ranging from forensic science, where it is used to detect bodily fluids and trace evidence, to artistic expression through fluorescent art and theatrical effects. Its use in security features, such as identifying counterfeit currency, highlights its importance in protecting against fraud. Historically, the discovery and understanding of fluorescence have contributed significantly to advances in spectroscopy and materials science.