Fluorescence

Fluorescent dyes absorb light energy and emit visible light of longer wavelengths (lower energy) than the absorbed radiation. In many cases, the absorbed radiation is in the ultraviolet range, so that a fluorescent solution will appear one color in transmitted light and a different color when viewed with a black light. Probably the most common fluorescent dye is fluorescein, which is added to commercial antifreeze to make it less likely that animals will accidentally drink it. Other examples of fluorescent dyes and pigments are rhodamine B and chlorophyll.