How Do Toys Glow in the Dark?

Radium dial glow in the dark (Source)

Remember when you glow in the dark toys were all the rage as a kid? And I were bouncing balls and plastic bugs and those little green stars that everybody stuck on the ceilings. I totally did that. So you have to ask as a member of the human species, "how do they work?' Some TV commercials claimed magic, but it's really thanks to these chemical compounds called phosphorus. Phosphorus is a substance that absorbs energy from another source, like a light for example and then amidst that energy as visible light which is the glow we see. There are natural phosphors in your teeth and fingernails which are why they glow after absorbing energy from a black light. But chemists have also created lots of phosphors and the most common ones, and glow-in-the-dark toys are zinc sulfide and strontium aluminate.

Zinc sulfide is really safe and affordable which makes it great for mixing in the plastics to make glow in the dark toys. Strontium aluminate is more expensive, but it has a longer persistence, which means it emits visible light more slowly, and glows longer after being energized. And both of these fosters naturally emit the greenish light. You know that pale iconic you.

Manufacturers can make other glow in the dark colors by adding different pigments to the plastic. Because you energized these toys with light, whether it's the Sun or a lamp in your living room, we say that there is photoluminescence. But not all glow in the dark things works like that. Glow sticks, for example, work by chemiluminescence, which means that light is emitted as a product of a chemical reaction. When you crack a typical glow stick, you are allowing a hydrogen peroxide solution to react with diphenyl oxalate. This chain of chemical reactions releases energy which is absorbed by electrons in fluorescent dye molecules that are also in the tube. That energy is emitted as photons of visible light, and it's a different color depending on the chemical structure of the dye molecules. And some watches that glow in the dark work in a completely different way through radioluminescence. In those, the phosphor is actually mixed with radioactive elements, like radium, tritium, or promethium. That constantly energizes the phosphor to make it glow, without being dangerous to the humans using the watch. The radioluminescence is rarely used nowadays because engineers are developing better photoluminescent compounds for watches as well.

So if you're the proud owner of a bunch of glow-in-the-dark stars or enjoy snapping some glow sticks on a dark night, hopefully now you have a better idea of how they work. Thanks so much for reading and don't forget to subscribe to our newsletter. Bye!