The Many Uses of the Neon Lamp

Neon lights are that kind of nostalgic item that everybody seems to love. The neon lamp is a type of gas discharge lamp, they generate light when an electrical discharge travels through an ionized gas, or plasma. When the voltage between the electrodes exceeds certain threshold, the gas ionizes and begins conducting electricity. The basic process that generates light is the return of the ions to the ground energy state, with the emission of a photon of light. The light color depends on the emission spectra of the atoms in the gas, and also  on the gas pressure, among other variables.  Gas discharge lamps can be classified by the pressure of the gas:

  • Low pressure: includes the neon lamp, fluorescent lamps and low pressure sodium lamps.
  • High pressure: such as the metal halide, high pressure sodium and mercury vapor lamps.

Another classification comes from the heating method of the cathode:

  • Hot cathode lamps: the electric arc between the electrodes is created via thermionic emission, where electrons are expelled from the electrodes because of the high temperature.
  • Cold cathode lamps: In these, the electric arc results from the high voltage applied between the electrons, that ionizes the gas and conduction can take place.

High intensity lamps are another type of gas discharge lamp where a high power arc is formed between tungsten electrodes. Power levels of several kilowatts can be easily produced this type of lamp. Of course we can’t forget to mention nixie tubes, which are a type of cold cathode neon lamp, popular for building retro clocks. Fortunately, they are now in production again.

History

852px-geissler_tubes_switched_on
A modern version of the Geissler tube.

The history of the gas discharge lamp starts in 1675, when Jean-Félix Picard, a French astronomer, observed that the empty space of his mercury barometer emitted a faint glow as the mercury jiggled. Later, it was showed that the glow came from static electricity in the partial vacuum in the mercury tube. In the 19th century, with the advent of electrical generators, several scientists started to experiment with gas tubes and electricity, resulting in the invention of the Geissler tube, by the German physicist and glassblower Heinrich Geissler in 1857. These were the first gas discharge tubes and were mass-produced mainly for entertainment purposes.

 

The neon tube, as we know it, was developed by a French engineer,  Georges Claude in 1910, and first demonstrated in the Paris Motor show of that year. In the US, the first neon signs were acquired by a Packard car dealer in Los Angeles, for $1250 apiece. Since the tubes can be produced in almost any shape, they are visible even in daylight, and a large number of colors can be created by different combinations of gases and coatings in the tube, neon signs quickly became very popular. By 1940, there were around 2000 shops producing neon signs in the US.

Relax

600px-ac_powered_ne-2_type_neon_lamp_close-up
NE-2 type neon bulb.

But neon lamps are not only decorative items. A small version is used today mainly as indicator light in electronic instruments and appliances, but it was important in the history of electronics. The neon bulb has negative resistance: before reaching the breakdown voltage, the lamp conducts almost no current. When the breakdown, or turn-on voltage is reached, the lamp’s resistance suddenly drops and a large current is established. In this condition, the voltage drops with increasing current. Therefore the turn-off voltage is lower than the turn-on voltage. This property is called hysteresis.

 

Because of this property, neon bulbs were used in relaxation oscillators, that can reach maximum frequencies of around 20 kHz. The neon lamp in the circuit does not conduct until the voltage of the capacitor reaches the turn-on value. Then the lamp starts to conduct and the capacitor quickly discharges until its voltage is the turn-off voltage of the lamp. The neon lamp stops conducting and the process repeats.

relax
Relaxation oscillators with neon lamps.

Neon lamps were also used as voltage references and overvoltage protection devices, taking advantage of their characteristic turn-on voltage. Also, with special fabrication techniques, they can also work as voltage regulators.

Neon Lamp Memory

Computing can also be done with neon lamps! In the circuit shown at the left, taken from the GE low lamp manual, we can see a simple memory circuit. According to the manual, it works in the following way: the supply voltage V is between the turn-on and turn-off voltages of the lamp, so that in the quiescent condition the lamp is not conducting.

memoryIf a positive “set” pulse is now applied to the input the lamp will fire, and with the supply voltage greater than the turn-off voltage, the lamp will remain conducting. To read out of the memory, a positive “read” pulse is applied to the input, with an amplitude less than that required to fire a non-conducting lamp. If the lamp has been previously fired by a “set” pulse, the “read” pulse will be passed through the lamp to the output. However, if the lamp has not been fired the “read” pulse will be blocked by the non-conducting lamp and the output will remain at zero. To reset the memory, a negative “reset” pulse is applied to the input, with a magnitude sufficient to drop the voltage below the turn-off voltage of the lamp.

The use of neon in electronic circuits is, of course, from an era that preceded silicon. The use in lighting had its peak in the 60’s, and started to fade after that. Modern types of lighting (you guessed, LED) are preferred for advertising. Nowadays, neon is experiencing a comeback as an architectural and artistic element, and also in some historic projects such as the Route 66 Corridor Restoration Act. We hope it stays with us for the years to come.

38 thoughts on “The Many Uses of the Neon Lamp

  1. The British Bell Punch/Sumlock Comptometer ANITA made extensive use of neon logic, mostly in the form of Dekatrons, and using the Nixies in the display as a memory element, but there were other logic circuits using discrete lamps in the unit.

  2. Lets agree that Neon is a type of gas discharge tube in lamp form… and not a Nixie… and that other cold cathode displays are not always Nixie (vacuum flourescent) and that other types of multi-segment digit displays are not Nixie but are cold cathode discharge indicator displays. We should agree that many *decimal* displays using the cold cathode discharge characteristics of neon corona glow are actually in fact called Nixie tubes. We seem to love calling all retro displays in glass cases Nixie… which drives us geezers nuts.

  3. Some of my fondest memories include designing–and playing around, of course–with neon lamps got that bee in my bonnet about six months ago, and embarked on a mission to find my old manuals. I did nor win (even though I uncovered two Sarkes-Tarzian selenium rectifier manuals (!); and a complete set of Atari documentation, including five pounds of Technical Reference Notes); only a Signalite document. A lot of really good application notes and instruction came from the neon-tube manufacturers.
    Manuel, if you can give us all a fairly complete bibliography, I, and many others, would be eternally grateful.
    Keep up the good work.

      1. Yes indeed, thank you.

        One thing: on the cover of the manual there are several neon lamps with three electrodes, but no mention of them in the book. Does anybody have any idea how this was useful?

        1. I’ve asked that question myself and gotten a variety of answers. Everything from mini-thyratrons, uses in logic circuits, and failsafe indicators but the only application that anyone could show a working example of was it being used as a two-level indicator in a heating unit.

  4. Years ago, I used the little neon indicator bulb as a light detector. Maybe you have noticed that the flickering neon indicator on some equipment will stop flickering if covered, and the flicker will become steady in strong light. Light, as a radiation source, makes ionization easier. Kind of like a Geiger tube.

        1. Yeah, I’m already turning those screws in my mind…
          Lots of carbon-blacked tubes and maybe a pinhole camera setup. Calibration: a ‘photo’ of complete darkness; If I can’t get it to detect light at least I can make an awesome display. Too many ideas, too many projects, full time real job…

          [Manuel Rodriguez-Achach] Thanks for the pdf and fantastic article!

          1. What’d be cool is a “digital” camera, where the neons don’t just detect light, but stay lit when they do. So you’d be able to see the image on the lamps themselves.

            Have the back of the camera removable for that, and a lens on the front side, point it at something, then take the back off to see your picture. Seems like it’d work, right? Using the neon memory effect mentioned in the article. You’d probably have to take simple pictures of chunky, contrasty things, but might get some results out of it. Perhaps a variable voltage for the power supply, to tune it just right. That’d be your “ISO” setting. You might have to take Victorian-style long exposures. Some setup required!

            This could be great!

  5. Thank you for this article. I love gas discharge lamps of all types, so this article is right up my alley.
    I was previously aware that neon bulbs could be used as part of oscillator circuits, but I was not aware that they could be used as memory elements! Thanks for expanding my knowledge base.

  6. I remember a story where an early computer was built with neon tubes as flip-flops. They noticed that for long computations that took all night, the results were wrong.

    When they investigated, they realized that the breakdown voltage was different when light hit the tube. At night, they normally switched the overhead lights off, causing the breakdown voltage to be different, which meant some circuits would not fire properly.

    The answer: keep the lights turned on at night.

  7. About 45 years ago, there was a cute exchange student from USA here in Oz. I made her a “Do Nothing Box” for her birthday in a translucent plastic box with a green lid (used for serving butter) and delivered in a plain brown paper bag.
    It was 3 lots of 10M resistor/NE2 series elements across a 90V battery, (you used to be able to buy small 45V batteries then) with 0.1uF capacitors connected from the junction of the R and Neon, not across the neon, but to the junction of the others. So there was a ring of 3 caps in the middle, with each neon to -ve and each 10M resistor to +90V. I hope that makes sense.
    Anyhow, the neons flashed as in the relaxation osc above, but one after another. It looked pretty good.

    Well, it worked! It is the morning here and I’m about to take her a coffee. After she went home at the end of her exchange, I saved up and flew there for a visit. We got married and I brought her home to Oz.
    So neons have a special place in our family :)

    1. Sweet! Here in the US Radio Shack had a line of little box kits called “P-Box” which came in a plastic box whose top was a serviceable breadboard. One of the P-Box kits was an “idiot box” which could be built in two ways, either with the five neons flashing randomly or with them flashing sequentially as in your gift to your girl. No 45V batteries though, so the kit also included parts for a little transistor oscillator and transformer to up-convert 9V to Neon levels. I built mine to flash randomly :-)

  8. There was a book our library had, something like 30 Electronic Games and Toys, and I felt kind of cheated by it, because every other project was abusing some property of an NE-2…. and the other ones got “clever” with triacs, barely a transistor to be seen.

  9. Lest we all think that neon glow tubes only radiate in the ‘orangey” part of the spectrum–
    I still have, in my “extremely-valuable-while-being-extremely-useless” junk box, a green neon tube–about the same form factor as an NE-2–given to me by sales rep in the 1970s. This was right around the time the the opto-semi people were announcing new LED colors on a semi annual basis.

    1. When I was a child (in the ’70ies) I had a green night light. It contained a glow lamp, but I remember that it emitted a blueish glow on the end and had a white coating on the inside. obviously a mercury vapor discharge and a green phosphor.
      But the designer got really cheap on the indicator lamps of a freezer: The plastic casings were red yellow and green, but each contained an orange neon tube. What looked not very god especially in the green one.

  10. Wow! This is awesome! I am really glad this topic came up! Ok, so the waveforms in a pulsed plasma field generated by conducting electricity through a gaseous state can and will have effects on biological organism.
    In much the same way the UV spectrum can alter parasites or bacterium, the pulsed plasma fields can eliminate entire species from the earth with a waveform.
    After researching it, I can say quantum entanglement explains the eradication of the fire ants. It also works on cancer! And black mold!
    I am limited in understanding details, or specifics, but certain gases look cooler than others, the plasma spark inhibitor is designed for the US military in Russia, the pulsed plasma emitter is owned and patented by a US citizen, but cannot be replicated. Its unique. That being said, there is a lot of science here that needs to be replicated. Rotational Plasma Fields might be a cure, or a weapon, or a propulsion system. Or a cool light show? Just know that the answer here is in the patent trail. Seek out the research, find the patent, talk to the current owner and see the truth. If I give the link you won’t appreciate the journey which leads to the questions. If you go down the rabbit hole, please explain to me the body electric so I can understand it. Its so over my head but so very cool!

    1. About the only thing you could do is an odd crossover between a tube distortion and a diode distortion. Classic tube distortion works by over driving the signal until it oversaturates vacuum tubes and clips. Diode distortion (Marshall will actually use LED’s) works similarly except using lower voltages and diodes instead of tubes.

      If I had to guess, you are going to get a lot of (not pleasant) noise and a muddy response off of these. Depending on how clean you can make your circuit boards, you’d probably run into odd harmonics due to the innate capacitance of any circuit board and possibly a hum if things aren’t biased right.

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