How Do Glowsticks Glow?
Picture an atom. Now picture that atom getting excited. Maybe its birthday is coming up. Anyway, when an atom or a molecule gets excited, its electrons' energy levels go up. When the electrons fall back down to their normal state, they release energy in the form of photons, a basic unit of light.
For most of the lights we make and use, those excited atoms release heat as well as light when they’re coming back down. Sometimes you want the latter without the former, a “cold light” like the kind made by fireflies. In the early 1960s, U.S. military and industry scientists knew that the key to making cold light on their own was chemiluminescence, the emission of light from chemical reactions. They just weren’t sure which materials and reactions they were after (luminol had been around for a little while, but had limited applications).
Edwin Chandross, a chemist at Bell Labs in Murray Hill, N.J., was one of the researchers working on the problem.
He wondered if peroxides – chemical compounds with an oxygen-oxygen single bond that could potentially liberate a lot of energy in some reactions - might do the trick. He tried a few experiments and found that hydrogen peroxide combined with oxalyl chloride and a fluorescent dye produced the cold chemical light he was after. The reaction’s efficiency was only about 0.1% (far short of fireflies’ near 90%), but it was a start.
Chandross began corresponding with Michael Rauhut at American Cyanamid in Stamford, Connecticut, and Rauhut’s team expanded on Chandross’ research, searching for ways to make the light bright enough for practical use. They eventually came up a diphenyl oxalate ester that reacted with hydrogen peroxide to make a bright light, trademarked their creation as Cyalume, and rolled it out on the market.
The reaction that happens inside a glowstick goes a little something like this:
- The typical glowstick contains an oxalate ester and dye solution within a plastic stick, and hydrogen peroxide within a small, fragile vial in the middle of the stick.
- When you bend the stick, the vial breaks open, and all the chemicals come together. The oxalate ester and hydrogen peroxide react, sometimes with the help of a catalyst, to form a peroxyacid ester and phenol.
- The peroxyacid ester decomposes to form more phenol and carbon dioxide, producing energy that excites all the molecules floating around in this little party, which then release photons, making the stick glow.
Since the glowstick’s invention, researchers have been fiddling around with this reaction, searching for fluorescing dyes to make different colors (green and yellow are said to be easy to make, while a good purple is near impossible) and adjusting the concentrations of the chemicals to brighten the glow or prolong its life.
American Cyanamid eventually sold its chemical light division, Omniglow. The R&D department there has continued to expand the uses and capabilities of glowsticks, creating luminescent intubating scopes and researching more efficient reactions and glow sticks that work at below-freezing temperatures.