Keep in mind that we are only presuming that the lamp is pure neon gas. The actual composition is quite unknown, the pressure is totally unknown, and what the electrodes are made of is unknown, but should be presumed to be cheap. So given the number of unknowns, the other unknown is "the eyes of the beholder." Perhaps they are more sensitive to whatever wavelength is being radiated. One equation with at least 5 unknowns is unlikely to produce a very definitive answer.

 

Allow me to give a brief recap: When plugged in, the neon lamp lights up. After being on all night WITH water in the reservoir, when pulling the plug the lamp continues to give off a glow. Not a bright glow, but a noticeable glow anyway. Keep this in mind, water boils at about 203˚F my elevation. The lamp is at the top of the head unit though not in the steam stream. Read that carefully please - the lamp is not in direct contact with the steam. However, the head unit can be so warm that you don't want to hold it for a long long time. You can tolerate touching it and removing it from the main reservoir, but if you have to carry it from the bedroom to the kitchen for a cleaning or refill right after running it all night - it's pretty warm. Under that condition, just yesterday morning, before the house heater came on, the room temperature was 67˚F. The unit had been on all night steaming away. When I unplugged it I watched for over four minutes and the lamp continued to emit a visibly detectable glow. I had to place my eye directly over the lens and wag my head side to side to determine that I was actually seeing a light source.

It was the day before yesterday that I left the unit running all day, and the tank emptied to the point where it was no longer in contact with any water. The sun had set and the room was dark. The lamp was on but the unit was stone cold (room temperature, approximately 72˚). When I unplugged it to take the tank to the kitchen for refilling - I unplugged it and watched the lamp go out. Within a few seconds, around 3 or 4 seconds I could not detect any glowing of the lamp whatsoever - even though it had been plugged in for about 22 hours.

In summary, when the unit is hot and unplugged, the lamp emits a detectible glow for in some cases over four minutes. When the unit is cold, and then unplugged, the lamp extinguishes within a few seconds. The only difference has been the heat. My conclusion is that the lamp is getting hot enough to glow. When at room temp it glows for a few seconds. When at near steam temp it can glow anywhere from a minute and a half to over four minutes. The longer duration measured involved me sitting with my eyeball about a quarter to a half inch from the lamp.

When I said it continued to glow I meant it would glow about 10 to 20% of its full brightness, down to maybe 3%. By no means a useful level of light, and this had to be viewed in a dark room after all sunlight was gone. Keep in mind these numbers (%) are just estimates and are subject to individual interpretation. Nevertheless, I noticed the lamp glowing after being unplugged. THAT is what prompted me to ask this question.

Thank you all for your contributions.

 

Tony, earlier in the thread I posted some images of small neon lamps and how they react to AC and DC current. Does your neon lamp look anything like them? If yes, then when faintly glowing is it one or both elements?

I can find plenty of references to how dark will effect the ionization of gas in the envelop but can't find any references to temperature making the gas glow without any electrical stimulation (lamp unplugged). Most standard neon lamps use a mix of neon and a small percentage of argon. Once I find and if I find a neon bulb around here it's going in the oven!

Ron

 

I think that shining a light on the neon bulb will add a bit of energy , I have observed very old "night lights" that go out in the dark but will start glowing if any light hits them. And then when it gets dark again they go back out. Part of that is because the series resistor value has increased. From this it is clear that it is the totall energy from all sources that allows the glow.

 

@Reloadron yeah, saw those pictures. I would assume (I said "Assume") both electrodes inside the neon bulb glow. The bulb is underneath a semi-transparent green lens. I can not directly see the bulb to answer your question, but I would assume both electrodes glow when energized. When power is removed I would have expected a complete cessation of all light production. I was surprised to notice a faint glow still going on. And at that - it glowed for quite some time after removing power.

In order to answer your question definitively I would have to open the head unit and plug it in. That would present a very hazardous situation as the boiler compartment would expose the electrodes as well as the electrical connections where the neon lamp and resistor are. I'd rather just assume both electrodes are glowing.

I have in the past fed neon with DC and observed that only a single element would glow from the power source. I've reversed the DC and found that the other element alone would glow. I've removed the diode and both elements glow (did this experiment in years gone past).

The ONLY thing I can understand is the presence of heat inside the bulb causing it to continue to emit a small amount of light. Perhaps some early morning I may decide - after a full night of steam production - use my cell phone video camera to see if the phone can detect the light. I could then post a video showing the faint amount of light it produces long after power has been removed.

As for the sort of neon lamp - - - I don't think I could tell one from the other except maybe for size. It looks like a very common and very cheap neon lamp. Its sole purpose is to be a night light. And at night when I sleep I prefer NOT to have a light lit. I like it very dark. Hence, being able to see a faint glow. HECK! For all I know it could be the plastic lens glowing. Maybe there's some phosphorus luminescence inside the lens. THAT can't be ruled out. Well, actually, I suppose I could expose it to bright light then turn out the lights and see if the lens glows. But any other testing with the lens removed would expose hazardous electrical energy. I'd rather not. But as far as the lens is concerned, I don't think it has any after-glow properties. If so I would expect it to be brighter. AND would expect the whole lens would glow, not just a faint spot beneath the lamp.

 

@Reloadron yeah, saw those pictures. I would assume (I said "Assume") both electrodes inside the neon bulb glow. The bulb is underneath a semi-transparent green lens. I can not directly see the bulb to answer your question, but I would assume both electrodes glow when energized. When power is removed I would have expected a complete cessation of all light production. I was surprised to notice a faint glow still going on. And at that - it glowed for quite some time after removing power.

In order to answer your question definitively I would have to open the head unit and plug it in. That would present a very hazardous situation as the boiler compartment would expose the electrodes as well as the electrical connections where the neon lamp and resistor are. I'd rather just assume both electrodes are glowing.

I have in the past fed neon with DC and observed that only a single element would glow from the power source. I've reversed the DC and found that the other element alone would glow. I've removed the diode and both elements glow (did this experiment in years gone past).

The ONLY thing I can understand is the presence of heat inside the bulb causing it to continue to emit a small amount of light. Perhaps some early morning I may decide - after a full night of steam production - use my cell phone video camera to see if the phone can detect the light. I could then post a video showing the faint amount of light it produces long after power has been removed.

As for the sort of neon lamp - - - I don't think I could tell one from the other except maybe for size. It looks like a very common and very cheap neon lamp. Its sole purpose is to be a night light. And at night when I sleep I prefer NOT to have a light lit. I like it very dark. Hence, being able to see a faint glow. HECK! For all I know it could be the plastic lens glowing. Maybe there's some phosphorus luminescence inside the lens. THAT can't be ruled out. Well, actually, I suppose I could expose it to bright light then turn out the lights and see if the lens glows. But any other testing with the lens removed would expose hazardous electrical energy. I'd rather not. But as far as the lens is concerned, I don't think it has any after-glow properties. If so I would expect it to be brighter. AND would expect the whole lens would glow, not just a faint spot beneath the lamp.

Now I am wondering if there may be something else "underneath a semi-transparent green lens." that is delivering the glow. Opening the head of that device would probably be destructive, as I imagine that it is not intended to ever need service.
So I am going to suggest chasing after more burning questions, such as:" has the solar energy output of the sun increased by perhaps 0.001% in the past few years?" Or in the past 50 to 100 years. AND, what is the meaning of the extended lack of sunspots for the past year and a half? And what are the implications if we discover that our climate change is the result of a small change in the sun?

 

My son, when was 2y. old, names all indicator lights "neon",
does not matter, what is color and light source.
Good test on real age...
EDIT: Age of brain.

 

OK, this is going on long enough! Going to take some pictures of the head unit and disassemble it and take more pictures. Will post shortly.

 

Pictures!

First, let me say when I opened it to clean it - I wasn't looking intently to see specifically what was there. What I saw was a neon type bulb. After opening it and taking photographs, it appears there's some sort of coating inside the bulb. Still, that doesn't change the fact that when it's cold but been on for hours it extinguishes almost instantaneously but when it's been on for hours AND the unit is still hot - the bulb doesn't extinguish for minutes.

img_1306 = Unit powered on tank.
img_1307 = Head unit
img_1308 = Cover removed
img_1309 = Flipped around
img_1310 = Lens removed
img_1311 = Bulb (with internal coating)
img_1312 = Bulb lit
img_1313 = Resistor = 22KΩ (Red Red Orange) (except the possibility I'm color blind and my screen isn't rendering the colors correctly)

 

So, now, assuming the coating inside the bulb is some sort of phosphorus coating, it glows when hot but not when cool. But I've never heard of a neon bulb with phosphor inside it. And I'm even wondering if the coating inside the bulb is some sort of oxygen gatter result, like in TV tubes. Never seen a neon with gatter in it. Oh well.

 

This coating is fluorescence dye.
Inside lamp - mercury vapor, UV exciter.
Dye is solid body, therefore it has long lasting afterglow.
Time of afterglow depends from temperature.
No neon, only mercury vapor.

And I'm even wondering if the coating inside the bulb is some sort of oxygen gatter result, like in TV tubes.

This "gater" is condensed mercury vapor.

Any indicator light is "neon" .

TS motto: "What is truth? It is accurate, complete and reliable information."

 

That is a fluorescent coating inside the bulb. Some examples here: https://www.jkllamps.com/incandescent/neonlamps

 

This coating is fluorescence dye.
Inside lamp - mercury vapor, UV exciter.

I would bet this is correct. It would be more accurately called a "neon style" bulb.

 

This coating is fluorescence dye.
Inside lamp - mercury vapor, UV exciter.
Dye is solid body, therefore it has long lasting afterglow.
Time of afterglow depends from temperature.
No neon, only mercury vapor.


This "gater" is condensed mercury vapor.

Any indicator light is "neon" .

TS motto: "What is truth? It is accurate, complete and reliable information."

Yeah, after seeing the lamp I am going with that. The neon gas is not producing an after glow but rather the fluorescence dye coating the glass envelop. That makes sense and Tony, thanks for the trouble of taking it apart again and for posting some very good pictures of the show. Now it all makes sense.

Ron

 

Never thought this thread would go 74 responses deep. Thanks all. And thanks for making me take it apart again just to know for myself why it glows after a night of operation.

 

Never thought this thread would go 74 responses deep. Thanks all. And thanks for making me take it apart again just to know for myself why it glows after a night of operation.

It was actually a really good thread which held interest, a why do it do dat!

Ron

 

But I've never heard of a neon bulb with phosphor inside it.

Have a look here:
https://en.wikipedia.org/wiki/Neon_lamp#Color

 

So, now, assuming the coating inside the bulb is some sort of phosphorus coating, it glows when hot but not when cool. But I've never heard of a neon bulb with phosphor inside it. And I'm even wondering if the coating inside the bulb is some sort of oxygen gatter result, like in TV tubes. Never seen a neon with gatter in it. Oh well.

The phosphor coating is used to change the color of the bulb. UV from the gas (usually a Argon mixture) discharge causes the fluorescent coating to glow. The coating looks whitish when not glowing.

https://forum.allaboutcircuits.com/...after-being-unplugged-why.165311/post-1455847

 

The phosphor coating is used to change the color of the bulb. UV from the gas (usually a Argon mixture) discharge causes the fluorescent coating to glow. The coating looks whitish when not glowing.

Argon+Mercury mixture.
First argon strikes the arc, this heats up and vaporizes mercury stuck to the sides.
The arc then goes through mercury vapor, which creates UV light.
The UV light excites the colored phosphor and you get your desired colored light.

 

So, now, assuming the coating inside the bulb is some sort of phosphorus coating, it glows when hot but not when cool. But I've never heard of a neon bulb with phosphor inside it. And I'm even wondering if the coating inside the bulb is some sort of oxygen gatter result, like in TV tubes. Never seen a neon with gatter in it. Oh well.

Yes, the white material is a phosphor of some kind, the bulb is probably filled with argon, producing ultraviolet that excites the phosphor. And the phosphor does keep glowing for a while, in proportion to the energy level some of it's atoms have been raised up to.

I really hope that you can get the thing back together and working again. The unit We had was the same principle, but the housing was ceramic and the thing was held onto a glass jug by what looked like an overgrown Mason jer ring. That was back in 1956, I believe. Same principle, older manufacturing processes.