How Do You Make Things Glow In The Dark?

With glow-in-the-dark toys, the phosphor mixed in with plastic is usually going to be zinc sulfide or strontium aluminate, according to HowStuffWorks. Strontium aluminate, the newer of the two substances, is especially powerful, with a glow that can last several hours.

Some items — particularly old watch or clock faces — have a consistently glowing screen that doesn't require charging. This is also created from phosphors, but with the addition of a radioactive material like radium or tritium that consistently charges the phosphor in place of a light source.

Ideally, this radioactive element is used in such small amounts that it isn't dangerous for the person wearing or making the glowing item. This hasn't always been the case, however. In the early 20th century, many workers in clock factories making radium dials eventually became stricken with radiation poisoning, according to Britannica. The resulting scandal eventually led to the creation of the U.S. Occupational Safety and Health Administration.

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