To make most glow-in-the-dark products glow, first you have to "charge" them by holding them up to a light for about 10 minutes. The reason they glow is because they contain phosphors; these are substances that radiate visible light once energized. The phosphors in glow-in-the-dark toys - - often zinc sulfide and strontium aluminate - - can be energized by regular light. Some objects glow even without charging, like the painted hands of some watches. The phosphors in these objects have been premixed with a radioactive substance that continuously energizes the phosphor.
How is technology a "resource liberating mechanism"?
Answered by Steven Kotler of Abundance
What U.S. law enforcement agencies oversee counterterrorism?
Answered by HowStuffWorks
How did you get interested in technology?
Answered by Megan Smith and John Perry Barlow