# What makes my watch hands glow? **URL:** \ **Category:** Factual Questions\ **Created:** [October 9, 2001, 12:48am UTC](https://boards.straightdope.com/t/what-makes-my-watch-hands-glow/86220 "2001-10-09T00:48:04Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![keithripploh](https://avatars.discourse-cdn.com/v4/letter/k/3bc359/32.png) [@keithripploh](https://boards.straightdope.com/u/keithripploh)\ **Post date:** [October 9, 2001, 12:48am UTC](https://boards.straightdope.com/t/what-makes-my-watch-hands-glow/86220/1 "2001-10-09T00:48:04Z")
I was wondering if you could tell me what the hands in my watch are made of, which makes them glow in the dark. I was told by my chemistry teacher that they are now using a new substance in these watch hands to make them glow. I was wondering if you could please help me out??? What is this substance? ---
**Author:** ![AgentofEvil](https://avatars.discourse-cdn.com/v4/letter/a/d6d6ee/32.png) [@AgentofEvil](https://boards.straightdope.com/u/AgentofEvil)\ **Post date:** [October 9, 2001, 1:00am UTC](https://boards.straightdope.com/t/what-makes-my-watch-hands-glow/86220/2 "2001-10-09T01:00:06Z")
I heard it was radium, but I could be wrong. ---
**Author:** ![Hello\_Again](https://avatars.discourse-cdn.com/v4/letter/h/85e7bf/32.png) [@Hello\_Again](https://boards.straightdope.com/u/Hello_Again)\ **Post date:** [October 9, 2001, 1:02am UTC](https://boards.straightdope.com/t/what-makes-my-watch-hands-glow/86220/3 "2001-10-09T01:02:29Z")
I always thought it was radium, but apparently that was the bad ol’ days. According to this site [http://www.wonderquest.com/GlowInDark.htm](http://www.wonderquest.com/GlowInDark.htm) it is a substance called phosphor. ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [October 9, 2001, 1:04am UTC](https://boards.straightdope.com/t/what-makes-my-watch-hands-glow/86220/4 "2001-10-09T01:04:37Z")
Your personality. (Just kidding. I’m not that good a judge of character.) Many watches have tritium dials. If you look at the bottom of the dial and it says “T 25” or “T~25”, then it has 25 microcuries or less than 25 microcuries of radioactivity provided by tritium, respectively. I’m not sure of the half-life, but I think it’s about 12 years. My newest watch (bought in 2000) has a Super Luminova dial. This dial is not (AFAIK) radioactive, puts out more light, and should last longer than tritium. ---
**Author:** ![kniz](https://avatars.discourse-cdn.com/v4/letter/k/c37758/32.png) [@kniz](https://boards.straightdope.com/u/kniz)\ **Post date:** [October 9, 2001, 3:33am UTC](https://boards.straightdope.com/t/what-makes-my-watch-hands-glow/86220/5 "2001-10-09T03:33:47Z")
[list][list][list][list][list] **Chernobyl?** …:eek:… ---
**Author:** ![Kvallulf](https://avatars.discourse-cdn.com/v4/letter/k/898d66/32.png) [@Kvallulf](https://boards.straightdope.com/u/Kvallulf)\ **Post date:** [October 9, 2001, 5:53am UTC](https://boards.straightdope.com/t/what-makes-my-watch-hands-glow/86220/6 "2001-10-09T05:53:33Z")
Word of Wisdom #457. If it glows in the dark, don’t eat it. ---
**Author:** ![KeithT](https://avatars.discourse-cdn.com/v4/letter/k/e47774/32.png) [@KeithT](https://boards.straightdope.com/u/KeithT)\ **Post date:** [October 9, 2001, 6:52am UTC](https://boards.straightdope.com/t/what-makes-my-watch-hands-glow/86220/7 "2001-10-09T06:52:56Z")
Obligitory link to HowStuffWorks: > **[How does glow-in-the-dark stuff work?](https://science.howstuffworks.com/innovation/science-questions/question388.htm)** > > You can find glow-in-the-dark item everywhere these days. Have you ever wondered how these items produce their light? Find out the answer to that question in this article. To sum up that article, chemicals called _phosphors_ are painted on the hands of your watch. When light strikes them, the electrons in the phosphors get excited. They jump up to a higher energy state. When you turn off the light, there’s nothing holding the electrons up, and they eventaully crash down to their initial state… being energetic little electrons, they give off a little green glow as they fall. This can take several hours for the phosphors in some high-end watches; inexpensive phosphors used in cheacper watches, toys and such use up all their “excited electron energy” in just a few minutes. Tritium (a heavy form of hydrogen, with two neutrons) is a radioactive material sometimes mixed in with phosphors to create a permanent glow for some specialty watches. Tritium’s slow radioactive decay keeps the phosphor electrons constantly excited, so the watch never has to be exposed to light.