Science, Tech, Math › Science 12 Things That Really Glow in the Dark They range from fireflies to tonic water Share Flipboard Email Print Ali Majdfar / Getty Images Science Chemistry Chemistry In Everyday Life Basics Chemical Laws Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated December 03, 2019 Many objects, chemicals, and products emit light via phosphorescence. Some are critters for which glowing serves a purpose, such as fireflies, which glow to attract mates and to discourage predators. Others are radioactive substances, such as radium, which glows as it decays. Tonic water, on the other hand, can be made to glow. Here are some of the most famous things that glow in the dark: Fireflies Fireflies glow to attract mates and also to encourage predators to associate their light with a nasty-tasting meal. The glow is caused by the chemical reaction between luciferin, a compound produced in the tail of the insect, and oxygen from the air. Radium Radium is a radioactive element that emits a pale blue color as it decays. However, it is best known for its use in self-luminous paints, which tend to be green. The radium itself doesn't emit green light, but the decay of the radium provides the energy to light the phosphor used in the paint. Plutonium Not all radioactive elements glow, but plutonium is one of the radioactive materials that does glow. The element reacts with oxygen in the air, causing it to glow a deep red, like a burning ember. Plutonium doesn't glow because of the radiation it gives off, but because the metal essentially burns in the air. It's called being pyrophoric. Glowsticks Glowsticks or lightsticks emit light as the result of a chemical reaction or chemiluminescence. Generally, this is a two-part reaction in which energy is evolved and then used to excite a colored fluorescent dye. Jellyfish Jellyfish and related species often exhibit bioluminescence. Also, some species contain fluorescent proteins, causing them to glow when exposed to ultraviolet light. Fox Fire Fox fire is a type of bioluminescence exhibited by some fungi. Fox fire most often glows green, but a rare red light occurs in some species. Phosphorus Phosphorus, like plutonium, glows because it is reacting with oxygen in the air. Phosphors and phosphorus glow an eerie green. Although the element glows, phosphorus is not radioactive. Tonic Water Both regular and diet tonic water contain a chemical called quinine, which glows bright blue when exposed to black or ultraviolet light. Glowing Paper Whitening agents are added to bleached paper to make it appear brighter. While you don't ordinarily see the whiteners, they cause white paper to appear blue under ultraviolet light. Some papers are marked with fluorescent dyes that appear only under certain lighting. Banknotes are a good example. Try looking at one under a fluorescent light or a black light to reveal additional information. Tritium Tritium is an isotope of the element hydrogen that emits greenish light. You'll find tritium in some self-luminous paints and gun sights. Radon Radon is a colorless gas at room temperatures, but it becomes phosphorescent as it is cooled. Radon glows yellow at its freezing point, deepening toward orange-red as the temperature is lowered even further. Fluorescent Coral Coral is a type of animal related to jellyfish. Like jellyfish, many forms of coral either glow on their own or when exposed to ultraviolet light. Green is the most common glow-in-the-dark color, but red, orange, and other colors are also known to occur.