Answer to Question #3302 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 just bought a digital watch that I really love. I notice that it has a "glow in the dark" button. After the watch has been exposed to the bright light, the button glows for many hours (12 hours or more). Does that "glow in the dark" button contain any radioactive materials (radium or tritium) to make the button luminous that I should worry about. There are many toys and stickers that glow in the dark. Are those toys and stickers radioactive?

Let me begin with a disclaimer: Since you have the watch, and I don't, it is impossible for me to answer this question with complete certainty.

Nevertheless, as I read your question, it seems that your watch must be exposed to light before it will glow in the dark. This suggests that the glow is a chemical luminescence, and that it is not due to radioactive material. If the glow decreases in intensity during the time that it is kept in the dark, it is safe to say that the glow is not due to radioactivity.

The fact that the watch is digital makes it very unlikely that it would contain radium. In the United States at least, radium hasn't been used in watches since the 1960s. If it does contain radioactive material, the latter would probably be tritium. Relatively innocuous stuff.

Regarding glow-in-the-dark toys and stickers: Once again, if they have to be exposed to light in order for them to glow, they do not use radioactive materials. And if the intensity of the glow decreases over time in the dark, it is certain that they don't. Nevertheless, although I have never seen any, there are bound to be some antique toys, say from the 1930s and 1940s, that employed radioluminescent paint.

Finally, an editorial: How anyone could love a digital watch is beyond comprehension. An old analog pocket watch, now that's something else.

Paul Frame, CHP, PhD

Answer posted on December 16, 2003. The information and material posted on this Web site 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 Web site. 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.