lowest voltage neon tube?

[coppercone2]

Do they have low voltage neon tubes? I see some stuff come up for 28VDC but its unclear if its actually neon.

Usually they say around 50V. But do they have special ones?

If you don't know, then basically neon tubes have a minimum distance where they stop working, because of some laws. so you can't just make it smaller. But I thought maybe there was a special gas mix or something.

[Conrad Hoffman]

Not aware of lower voltage bulbs. 45-65V is typical. The voltage will rise in the dark, so if you can keep the bulb illuminated the striking voltage will be lower. Long ago I worked for a company that built electronic shutters. The controller used a neon bulb in the timing circuit, with another constantly on bulb right next to it for better stability. The ones with a bit of radioactive gas will strike lower but I don't know if those are still made.

[coppercone2]

lol I just want one that would strike at 40VDC so I can put it on a impedance analyzer with 40V bias

In a bright room for a small NE2 I get like 57 v.

[TimFox]

The Bourns "GDT" gas-discharge tubes are designed for this purpose.
Their standard product goes down to 75 V breakdown voltage, but the special units on page 14 of this brochure go down to 60 V.
See  https://www.bourns.com/docs/technical-documents/technical-library/gas-discharge-tubes/publications/bourns_gdt_short_form.pdf

[coppercone2]

no i mean I thought I could measure the plasma impedance . its just a little too high voltage though

[jonpaul]

Cu:

See the many classic texts on gaseous discharges.

Well characterized since 1800s

Best recent was Signalite

App notes
https://www.one-electron.com/Archives/Tube/Signalite/Signalite.html

book on Neon lamp applications:
Applications of Neon Lamps Gas & Discharge Tubes Lights Edward Bauman 

In brief: Strikingvoltage depends on gas comp, pressure and electrode surfaces, as well as possible radiactive  doping
After ignition there are the glow and arc mode.

Glow has a cathide dark spce drop, positive column and anode spce.

The votage of the lamps is the sum od these effects.

Generally the minimum strike is ~ 60..70V. NE-2

Jon

[Zero999]

Put a violet or UVA LED next to it and give it a brief, high current pulse?

[coppercone2]

how much does that lower the ignition voltage to? I will try it actually. I am setup with a neon tube strapped to a hv power supply

[coppercone2]

striking voltage goes from 76v to 70v with a bright UV flashlight


small UV tube light has no effect basically (UVB)

[Zero999]

That's because the neon lamp's glass bulb blocks the shorter UV wavelengths.

[jonpaul]

Radioactive doping in the bulb increases prob of ignition

External UV needs to be very powerful, to create photoelectrons (see Einstein paper of 1900)

Neither will lower the ignition V.

j

[coppercone2]

it definitely lowers ignition voltage, I tested it. About 6 volts lower for a bright UV flashlight

[jonpaul]

statistical ...need to make a lot of tests to see if you have a random variation in strike V.

Arc or glow V is unaffected.

https://en.wikipedia.org/wiki/Photoelectric_effect

See J.J.Thompson qnd Ellenbass at Philips


j

[LaserSteve]

Let's agree to disagree. About 15 years ago I DID run the statistical  test.
For some versions of NE2 with the correct electrode material, Short  wave UV did lower the firing voltage by 5-10V.  Not only did it lower the firing voltage, on a current starved
NE2 I could change the region the glow started in
with a focusing lens or by moving a fiber optic probe.

Gas filled photodiode tubes do exist.
Steve

[coppercone2]

I am telling you I have a tube here attached to a power supply on the test leads. when I turn it up it strikes at 77V. When I shine a UV light on it it strikes at 73V. Repeatedly.


Yesterday it was a bit different in the thresholds

I can also keep it unlit at 74V unlit, and when I turn the light on it turns on.

It seems dependent on the polarity too, if I flip the bulb I get different voltages.

And now I got my 15W led PCB exposer (UV led 15V diode @ 800mA). I can turn it on at 66V when it normally trips at 74V.

You can make a UV triggered gate with this thing.



update did a experiment:

turned on UV bulb 5 times. Each time it lit 74-75V.

I turned it off and set PSU to 55V. I incremented one Volt and flashed it with the 385 nm 800mA LED. I got it to turn on at 60V. This is 14V less then the normal threshold. But its dim. And if you drip the voltage even a little to 59V, it turns off. But it does stay on. This is with a 250V sorensen PSU (250mA). The light source is a 750mA 15V LED on a CPU heat sink that is regulated by a current source configured LT3080 that is ran off 20AA batteries, and its inside a metal box. the 60V trip threshold is repeatable. I hold the light so the neon bulb is almost touching the diode. There is no optics, just a hole in the aluminum panel.

this is 15V lower. Once it turns on this low voltage, its so sensitive to variations that it will turn off if you bearly touch the knob, I mean like 1 degree rotation.
If you ignite the lamp properly at 74-75V, and then lower the voltage, it goes out at 60V. This is precisely the minimum point that you can turn it on with the bright UV light.



My observation is this: if you determine the glow range for this neon bulb, (trigger 75, shines down to 60), it is possible to trigger it at 60V with a bright flash of UV light. So you can turn it on the absolute minimum voltage range.


I got a second bulb from the same lot. It turns on around 75V DC and stays lit down to 60V. The same thing occurs, if I adjust it to approx 60V, and flash it with the light, it turns on. These are whatever bulbs that are meant to replace the bulb in harrison power supplies.

I think the results are pretty cool. 15V is quite a bit.

I am sorry to say I am convinced and that book must be wrong or defining something differently. But its a visible glow to the naked eye in a lit room. And its striking at the minimum of its operating voltage.

I tried it with another neon bulb, this time a blue one. IDK what it is, I think its phosphor, but its a neon bulb that glows blue. Strike voltage is 85V with power supply. I can get it to trip at 75V with the UV light pulse. This one looks frosted, so I guess its attenuating the light, you can't kick start it as low as the clear glass neon bulb.

Since it works on two different NE2 bulbs and the blue phosphor neon bulb, I am gonna say this definitely works, and it works better on bulbs without phosphor.

[tggzzz]

Somewhere online you can find PDFs of "Using and understanding miniature neon lamps" by William G. Miller.

That has tables of maybe 200 different neon's characteristics.

[Zero999]

This isn't something I've tested, but it's well-documented, hence why I suggested it.

Does it make any difference which electrode is exposed to more light?

I wonder if a higher intensity would help. You could try a Blu-ray laser. It's 405nm, so more violet, than UV, but is a much higher intensity, so could be more effective.

[mzzj]

it definitely lowers ignition voltage, I tested it. About 6 volts lower for a bright UV flashlight

Doesn't even need UV led. I see about 5 volt difference between brightly illuminated(white led)  and neon tube in dark ignition voltage.
No idea if this is gas/electrode temperature related, small amount of UV in white led output or what.

XHP50.2 flashlight with TIR reflector puts out stupidly high light intensity out of lens so thermal effects come to play also.
"good" also for lightning a fire to wood shawings, shrink..setting heat-shrink tubing on fire and burning holes in your pockets.
Lightbeam burns a hole in jeans in less than 10 seconds 

[CaptDon]

Nixie tubes are indeed doped with radioactive materials!! It was found early on that various nixie equipped meters and testers would not ionize in dark environments like mines and so forth. This was a big problem in multiplexed nixie displays!! Depending on drive circuitry and also the part number of the nixie there is at least one unused 'no-connection' pin that extends into the tube and because it is essentially a pinpoint electrode in the gas that will ionize more easily. It can be connected through a very high resistance (1M to 2.2M typical) to act as a 'keep-alive' cathode which lowers the strike voltage of the other cathodes. Some of the end view nixies have a peculiar internal structure that is connected to two pins and is not described in the nixie literature. I guess it is some sort of gettering electrode? There appears to be a white oxide coating on the element and the element looks like a tiny spring. It can be made to glow like a filament.

[coppercone2]

the only thing I have not ruled out is that its possible a EM field thats triggering it from the light. Maybe I can throw a piece of black card board on top of it to see if it triggers with the light blocked

[SeanB]

Gas discharge you will not get anything below around 60V unless you have heated filaments in there, which can get you down to very low voltages. Dope the filament with mercury, and you can get a discharge lamp that will operate off 24VDC, though it emits mostly UV light, as characteristic of a mercury discharge, with a little visible green light. But you will not find these commonly, though you can use VFD displays as well, as you can get visible light out of them as well, and the grid allows control, and they operate off around 3V for the filament, and anything over 5V will light the phosphor side.

[coppercone2]

i tried it with a box over the light, its not working. the light is doing it

How hot does it have to get? Can you get it hot enough by flowing hot air over it?  Not sure how much a NE2 can take before it fails structurally.

[jonpaul]

An arc or glow discharge needs a trigger to start.

The First trigger electron causes an avalance to start.

Source can be cosmic rays, natural radioactivity

 Cu has notice the effect of  light impinginmg on the electrodes 

 Einsteins photoelectric effect,

E=hf,

 E is the energy of a photon of frequency f and h is Planck’s constant.

the light frequency = 1/wavelegnth has direct proportion to the photon energy, thus shorter wave like UV gives more  energy and is more likey to ignite the glow.

Calibrated sphere gaps for HV measurement use a 2537 or 1849 A SW UV lamp shining on the spheres.

Enjoy,



Jon