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Neon lamp indicators embedded in power strip switches indicate whether the switch is ON or OFF.

When the neon lamp is ON in a dark environment (lights of the room are off) the lamp start to flickering and some times it goes off for a few seconds.

When I switch the lights of the room on, it stops flickering and remains bright. Even when I unlock my phone in the dark near the lamp, it stops flickering!

Is the mechanism of making brightness in neon lamps is related to the luminous intensity of the around environment?

enter image description here

UPDATE: I captured my observations with my iPhone and uploaded it to the YouTube. Here is the link of the video: https://youtu.be/1jlUmEfGHZA

All lights of my room was turned off. There was no connected plugs to sockets of the power strip. The only light was screen brightness of my MacBook Pro that was not connected to the power supply. I was decreasing and increasing the brightness of the screen during the video. The two last lights are the brightness of my phone.

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  • \$\begingroup\$ The light of gas discharge lamp is due to ionization, mostly caused by aceleration due to high voltage and collison of electrones with gas molecule. The ionization however can happen also due to external causes. \$\endgroup\$ – Marko Buršič Apr 24 '16 at 20:01
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    \$\begingroup\$ Maybe here is an another guy making some hypothesis arrond your thougts: technicaltom.wordpress.com/2013/09/14/… \$\endgroup\$ – Marko Buršič Apr 24 '16 at 20:09
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This is a common phenomenon: neon pilot lights have a limited lifetime, and after many years of use, they begin to flicker, then they finally go dark. They no longer can operate at line voltage, but instead require a higher voltage for stable operation.

Also, neon pilot lights can act as photosensors. Try this with a flickering neon bulb: shine a red LED on it. Then shine a blue LED on it. If both LEDs are roughly the same brightness, then the blue LED should have a much greater effect. You're seeing the same photoelectric effect that won Einstein the 1921 Nobel, leading to the "photon" concept.

All gas-discharge tubes suffer from a common problem: the gas atoms tend to become embedded in the metal surface of electrodes, so over many years the gas pressure falls as well as the gas mixture being altered.

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  • \$\begingroup\$ +1 for the wavelength dependant test suggestion to confirm the photoelectric effect. \$\endgroup\$ – KalleMP Mar 4 '18 at 7:55
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To quote from the great wiki - https://en.wikipedia.org/wiki/Neon_lamp

"When the current through the lamp is lower than the current for the highest-current discharge path, the glow discharge may become unstable and not cover the entire surface of the electrodes.[6] This may be a sign of aging of the indicator bulb, and is exploited in the decorative "flicker flame" neon lamps. However, while too low a current causes flickering, too high a current increases the wear of the electrodes by stimulating sputtering, which coats the internal surface of the lamp with metal and causes it to darken.

The potential needed to strike the discharge is higher than what is needed to sustain the discharge. When there is not enough current, the glow forms around only part of the electrode surface. Convective currents make the glowing areas flow upwards, not unlike the discharge in a Jacob's ladder. A photoionization effect can also be observed here, as the electrode area covered by the glow discharge can be increased by shining light at the lamp."

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  • \$\begingroup\$ To concentrate on the first sentence of your quote: "When the current through the lamp is lower than the current for the highest-current discharge path..."--how do you propose that this happens in OP's case? The line voltage is not likely to fall significantly just by turning on some lights, much less a battery-powered telephone or laptop computer. Also, it is not photoionization (nothing is being ionized), but rather the photoelectric effect. \$\endgroup\$ – Oleksandr R. Apr 25 '16 at 2:48
  • \$\begingroup\$ @OleksandrR. I don't propose anything, I'm simply quoting from the article. I would agree that the term used in the article should have been photoelectric rather than photoionisation (as in a GM tube). If you wish to correct and update the wiki article please feel free \$\endgroup\$ – JIm Dearden Apr 25 '16 at 12:50
  • \$\begingroup\$ @OleksandrR. The current will fall to zero 100 (129) times per second. The discharge path changes with age and at some point the peak line voltage will no longer achieve the minimum stable current path demands. \$\endgroup\$ – KalleMP Mar 4 '18 at 7:49
  • \$\begingroup\$ @JImDearden The GM tube does not use Photo-ionisation in normal function. It does not care about the work-function of the electrode surfaces. You are thinking perhaps of a Phototube en.wikipedia.org/wiki/Phototube \$\endgroup\$ – KalleMP Mar 4 '18 at 7:53
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Responding to old post but it comes up at top of google search:

Neon lights can't work in complete darkness. This is the "neon lamp dark effect".

I know it sounds fake, but that's why neon lamp bulb makers sometimes add a little ionizing radiation inside the bulbs.

Dark Effect: All ILT Neon lamps are subject to a condition called dark effect. Dark affect is defined as a drastic increase in the amount of voltage required to make a lamp glow when the lamp is in a dark environment. Because the lamp is photosensitive, it may require many additional volts to start if no light is present. Neon lamps can also become erratic in total darkness.

To prevent dark affect an external source may be run near the neon lamps or in some cases, custom Neon lamps can be supplied with a radioactive gas, often Krypton 85.

(Source: International Light Technologies, Inc. - ILT)

Yes it is bizarre and a trouble-shooting nightmare for the unaware, lol. But you can use a simple neon bulb as a photosensor. But also they do flicker more and more as they age and die: but they not really dead, they just need more power than the device gives. If you ramp up the juice (in a different device) they will work for a while longer.

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    \$\begingroup\$ Michael Welcome to the EE stack exchange. Please go to the help button and take the instructional tour. Good answer though +1. \$\endgroup\$ – RoyC Apr 1 '18 at 17:39
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There are some possibilities here.

1: You live in a house where somehow, weirdly, the power dips and unbalances when there is no use. That normally only happens with over-use, though.

2: You're like every single other person in the world and have working pupils and a normal human brain. (That may either be a relief to you, or a shock, I hope the prior).

Of course, there are some other options, but I'll explain the more likely number 2.


Step one to that is that our brains are amazing processors that know what is important and what is not in the context that they are seeing. We've trained them for millions of years to become good at that. So in normal conditions the flickering is unimportant and boring to your brain.


Step two is that in low light conditions your pupils widen, allowing a lot more of the light and differences into our eyes. Presenting, suddenly, a much stronger flicker to your brain in a dark environment with nothing else to process.


Step three is that your brain is also very good at fooling itself; you see what you think you see. If you start focusing on the Light your expectations exaggerate the actual flickering.


Step four is that any light source will create a huge amount of light compared to the Neon light, closing your pupils, removing the level of detail from the Neon light and also adding a lot of new information for your brain to focus on that seems more important. (Where the chairs are. Are there any feral cats under my desk? Did you get any new texts? Why has {insert cute girl [-or boy as far as I care-]'s name here} not responded yet?)


Step five is an actual thing that happens: The light turning off can happen once in a while through either the light wearing down, or having small moments of high levels of polarization in a place where there's little fluorescent material, so that all current flows there for a second or two creating nearly no light. This would logically also happen when the lights are on, but you may just not notice so much with a lot of light around you, since the event is not significant at all. Think about it: If you have 5000 Neon lights, and one pops off, how long would it take you to notice? If you have only one of those same lights, and it goes off suddenly, you're bound to see immediately: All your light is gone!


The fifth is helped by the Neon lights in power strips costing a negligible amount of money, as they are the cheapest kind of Neon light ever invented. 'You get the quality you pay for'.


All that said, of course, there may be a combination of several things going on. But I'm betting (heavily) on the flickering/no-flickering definitely just being a change in perception.

The Neon's in series with a load, such as in a wall light switch, can of course exhibit all kinds of strange behavior with capacitive loads, or inductive loads, or very light loads. But the Neon in a power strip is directly connected to the mains through the switch, in parallel with all other loads, so that's not happening here.

It might only 'spark a bit brighter or dimmer' just the once when you switch on or off a very heavy load, but that should be clear enough, in some buildings all the lights always do that.

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  • \$\begingroup\$ +1. OP could try monitoring the neon through a cardboard tube, blocking out ambient light, while someone switches load to see if the effect is real or perceived. \$\endgroup\$ – Transistor Apr 24 '16 at 20:04
  • \$\begingroup\$ @transistor But the OP says that the ambient light is the cause. If you block it, then it has no sense for such experiment. \$\endgroup\$ – Marko Buršič Apr 24 '16 at 21:28
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    \$\begingroup\$ @Asmyldof Thanks for your answer but this fact is not only sensible my eyes/brain/perception but also I captured it with my iPhone. There is no connected plugs to the sockets so maybe the load is constant. In addition, I saw this fact in other cities. So I think these steps 1-5 is not matching the fact. \$\endgroup\$ – Hamid Rohani Apr 24 '16 at 22:50
  • \$\begingroup\$ @transistor I think this is not related to the load. With a cardboard tube and without any ambient light, the flickering is observed. Even with a camera. \$\endgroup\$ – Hamid Rohani Apr 24 '16 at 22:58
  • \$\begingroup\$ @HamidRohani Why do you think the Auto-Gain on your iPhone is any different than your pupils? Who's looking at your iPhone, You or some omnipotent objective artificial intelligence? How did I ever imply any of these brain effects only happen in your house and not anywhere else in the world? \$\endgroup\$ – Asmyldof Apr 25 '16 at 6:54

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