Buzz
To activate a light stick, simply bend it to mix the internal chemicals and create a glowing effect.Glow-in-the-dark items are found everywhere, with toys being the most common. For instance, my son owns a variety of glowing toys, including a yo-yo, a ball, a mobile, and even glow-in-the-dark pajamas. These make him easily visible at night!
If you've encountered these products, you’re aware they require "charging." Expose them to light, then move them to a dark area. They’ll emit a soft green glow for about 10 minutes, with some newer products lasting several hours. The glow is subtle and best seen in near-total darkness.
Every glow-in-the-dark product includes phosphors, substances that emit visible light when energized. Phosphors are commonly found in TV screens or computer monitors and fluorescent lights. In TVs, an electron beam activates the phosphor (explained in How Television Works), while in fluorescent lights, ultraviolet light does the job. Both produce visible light. A TV screen has thousands of tiny phosphor elements emitting red, green, and blue light, whereas fluorescent lights use a mix of phosphors to create white light.
Chemists have developed numerous chemical compounds that act as phosphors. These substances share three key traits:
- The specific energy needed to energize them
- The color of visible light they emit
- The duration they glow after being energized (referred to as the persistence of the phosphor)
For glow-in-the-dark toys, the ideal phosphor is one activated by regular light and with long persistence. Zinc Sulfide and Strontium Aluminate are two such phosphors. Strontium Aluminate, used in "super" glow-in-the-dark toys, has a significantly longer glow time than Zinc Sulfide. The phosphor is blended into plastic and molded to create most glow-in-the-dark items.
Sometimes, you’ll notice objects glowing without needing a charge, like on high-end watch hands. Here, the phosphor is combined with a radioactive element, continuously energized by its emissions (detailed in How Nuclear Radiation Works). Historically, radium was used, with a half-life of 1,600 years. Modern glowing watches often use tritium (a hydrogen isotope with a 12-year half-life) or promethium, a synthetic radioactive element with a half-life of about three years.
