Wikipedia:Reference desk/Archives/Science/2018 November 17

= November 17 =

neon bulb as sensor
hello, I had this weird idea. does the breakdown voltage of a neon bulb (the kind used in phase testers, illuminated switches etc) depend at all on external conditions (temperature, incident visible light, UV, α, β, γ)? IOW, if I brought a neon bulb to a few mV below breakdown, could it detect stuff? or, better yet, if I made made an oscillator and measured the frequency (f-to-V), would it reflect something? Aecho6Ee (talk) 20:17, 17 November 2018 (UTC)
 * Yes.
 * Just what is a harder question. Neons, especially older ones, are sensitive to all manner of environmental factors. You can even use them as random number generators. Andy Dingley (talk) 22:44, 17 November 2018 (UTC)
 * Ionizing radiations such as gamma radiation, X-rays, and alpha and beta particles can all trigger electrical breakdown in a neon tube, as exploited for their detection in the Geiger–Müller tube. DroneB (talk) 15:54, 18 November 2018 (UTC)


 * "All manner of environmental factors", yes. How about light?  In a windowless room in the basement of my house there is a small freezer, 40 or 41 years old. In those days LEDs weren't yet in wide use, and its "on" indicator is a neon lamp.  At one time this indicator glowed steadily but now it always flickers.  Or, at least, "always" was what I thought until a couple of years ago, when I discovered that if the light in the room is turned off and the door closed, the neon lamp immediately shuts off.  Put the light on or open the door enough to let some light in, and it immediately starts flickering again.


 * I mentioned this effect to a friend, who said that this phenomenon is "mentioned on the Wikipedia page on Neon lamp (cf. photoionization)". --76.69.46.228 (talk) 07:14, 19 November 2018 (UTC)
 * Look particularly for this effect with those neons that are coated with phosphors to give different colours. The surface treatment makes them much more sensitive to photoelectric effects. Andy Dingley (talk) 11:47, 19 November 2018 (UTC)
 * The one thing you can't do with a neon is use it as a G-M tube. The pressure is too high, the distances too close. You can't raise them to the voltages needed to show the G-M cascade effect without a simple gross breakdown. Andy Dingley (talk) 11:47, 19 November 2018 (UTC)