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08 February 2012

Answer to Question #1473 Submitted to "Ask the Experts"

Category: Consumer Products — Watches, Clocks, and other Glow-in-the-Dark

The following question was answered by an expert in the appropriate field:

I have bought some phosphorescent shapes for my kids: stars, moon, planets . . . . Are they radioactive?

My three girls also have these—on their bedroom ceilings. If my wife wouldn't object, I'd probably have them in my bedroom as well. To answer your question, no, the luminescence is not due to radioactive material. If it were, the intensity of the light emitted by these things would remain constant. But it doesn't, their light gradually decreases in the dark. The light emission is a form of phosphorescence. As the stars, etc., are exposed to light from the sun or other light sources, the electrons associated with a particular chemical absorb some of the light's energy. The result is that these electrons are promoted to a higher energy level. Over time, in the dark, these electrons gradually fall back down to their original lower-energy state. When they do, they emit light. Sooner or later, they have all gone back to their initial energies and the light emission ceases. Paul W. Frame, CHP, PhD

Answer posted on 7 December 2001. The information and material posted on this website is intended as general reference information only. Specific facts and circumstances may alter the concepts and applications of materials and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice specific to whatever facts and circumstances are presented in any given situation. Answers are correct at the time they are posted on the Website. Be advised that over time, some requirements could change, new data could be made available, or Internet links could change. For answers that have been posted for several months or longer, please check the current status of the posted information prior to using the responses for specific applications.