Kryptonite is the longest lasting phosphorescent material available. It glows all night (over 12 hours) after charging in the sun for only an hour or two.
These tiny vials (about an inch high and half an inch in diameter) contain enough Kryptonite to read maps at night, or books under the covers.
No evil genius should be without a protective vial of Kryptonite! Keep one of these in your pocket, and Superman will keep his big "S" out of your business!
This makes a good sample for Strontium, Europium, or Dysprosium in your collection of samples for the Periodic Table of the Elements.