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General Science => General Science => Topic started by: neilep on 25/07/2005 21:14:21

Title: How bright do watch luminescent hands get ?
Post by: neilep on 25/07/2005 21:14:21

Dearest Science Wonderpeeeps,

You know how when you hold a watch up to a bright light it charges up and luminesces even brighter ?, well the hands do , or the numbers etc etc...is there a brightness limit to which these little specks of lighty joy can be charged up ?..in other words how bright can they get ?..are there varying degrees of luminescent orientated brigthness's when it comes to watch hands ? It's a radioactive thing yes ?..does that mean that over a period of years and years that the luminescent joy will wither and die ?

It's time to reveal in awe and shiny glimmers the answer to this query of light !

Thanks

neil


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Title: Re: How bright do watch luminescent hands get ?
Post by: chris on 26/07/2005 08:20:42

Hi Neil

the luminescence seen from 'glowing plastic' is a function of its ability to absorb photons of energy from light which excite electrons within the substance. After a while the electrons drop back to their original energy states, re-releasing the extra energy they absorbed as visible light. The better the material (referred to as a phosphor) at grabbing photons and then stably maintaining them in an excited state, the brighter and longer it will glow.

Radioactivity can be used to do the same thing, but is not essential. In this context you use the energy released by radioactive decay to excite the phosphor (temporarily boosting its electrons to a higher energy state) rather than visible light itself.

Here's a question of the week which I wrote last year about phosphors, glow in the dark watch and clock hands, and television sets (http://www.thenakedscientists.com/forum/topic.asp?TOPIC_ID=350&whichpage=7#13541)

Chris

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