Phosphorescence

Have you ever seen glow-in-the-dark stars on a ceiling? They use phosphorescence. Phosphorescent materials absorb light energy and then release it slowly over time. After the lights go off, they keep glowing for minutes or even hours. It is like the material stores light and lets it out slowly.

How It Works

When light hits a phosphorescent material, its atoms absorb the energy and get excited. Unlike fluorescence, where the energy is released almost instantly, phosphorescent atoms hold onto the energy longer. They release it slowly as a soft glow. The glow gets dimmer over time as the stored energy runs out.

Uses of Phosphorescence

Glow-in-the-dark toys, stickers, and watch dials use phosphorescent materials. Emergency exit signs in buildings often use phosphorescent paint so they glow during power outages. Some clock hands are painted with phosphorescent material so you can read the time in the dark.

Fun Facts

• The best glow-in-the-dark materials can glow for over 12 hours after being charged with light.
• Strontium aluminate is one of the brightest phosphorescent materials and is used in safety signs.
• Some deep-sea creatures use bioluminescence, which is different from phosphorescence because it is made by living things.

Did You Know?

Old glow-in-the-dark watch dials used to contain radium, a radioactive element. Workers who painted the dials got sick because they did not know radium was dangerous. Today, safe phosphorescent materials are used instead!