ECN Forum Forums General Topics of the Trade General Discussion Area exit signs

Sorry to go way off topic (to a degree), guys,
I was reading an article in the June 1988 edition of Electronics Australia (yes, I collect these mags) and the article was talking about Geiger counters.

What sparked my interest about this article was that the author mentioned things like clocks and watches that had "glow-in-the-dark" faces and hands.

Now, the author was talking about after WWII when ladies were working in the clock and watch-making factories of places like then-Russia, to apply the paint to the certain parts of the face, etc they would dab the end of the brush on the end of their tongues, to help get the paint (which contained all sorts of nastiness) to stick to the metal.
Thousands of women died later on, at quite early ages, through what was known as "Radium Jaw".

Apparently, if you can find an old clock or watch that has one of these faces on it, you can still get quite a high reading of radio-activity with a Geiger counter.
We never used to worry about this sort of thing years ago, mind you, we have gone digital since then.

My apologies if I've taken this thread too far off topic.

Yes, my dad told me that long ago, the part with the radioluminescent hands... but he also said they only emitted alpha rays already blocked by the glass. Of course if you ingest that stuff or get it into your mouth... ouch!

My current wrist watch seems to have had such hands once... but they don't glow in the dark any more, they just react to UV light. No idea how old it is, it's a quartz wristwatch my grandmother gave to me (it once belonged to my grandfather).

Mike,

Ottawa, Illinois had two factories that painted watches in the same fashion

http://www.roger-russell.com/jeffers/radiumdials.htm

There may be a good reason though. Many LEDs have a PIV (Peak Inverse Voltage) rating which is nowhere near as high as the PIV for a conventional silicon diode. When you run them on A.C., putting a diode in series will prevent the PIV of the LED from being exceeded.

I am guessing the LED exit sign has protective diode inside. I like one forward biased in front of the LED and another reverse biased across the LED but that is a belt and suspenders approach. This was in my "capacitor voltage drop" scheme on an SSR.