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Home » Mini Projects » Neon Lamps – Working and Application Circuits

Neon Lamps – Working and Application Circuits

Last Updated on November 20, 2021 by Swagatam 41 Comments

A neon lamp is a glow lamp made up of a glass cover, fixed with a pair of segregated electrodes and containing an inert gas (neon or argon). The main application of a neon lamp is in the form of indicator lamps or pilot lamps.

When supplied with a low voltage, the resistance between the electrodes is so large that the neon practically behaves like a an open circuit.

However, when the voltage is increased gradually, at a certain specific level where the inert gas inside the neon glass begins ionizing and results in being extremely conductive.

Due to this the gas starts producing a radiant illumination from around the negative electrode.

In case the inert gas happens to be neon, the illumination is orange in color. For Argon gas which is not very common, the emitted light is blue.

How Neon Lamp Works

The working characteristic of a neon lamp can be witnessed in Fig. 10-1.

The voltage level which triggers the glowing effect in the neon bulb is termed as the initial breakdown voltage.

As soon as this breakdown level is struck, the bulb is triggered into "firing" (glowing) mode, and the voltage drop across the neon terminals stays practically fixed irrespective of any kind of increase in current in the circuit.

In addition, the glowing section inside the bulb increases as the supply current is increased, until a point in which the total area of the negative electrode is filled by the glow.

Any additional escalation in current may then drive the neon into an arcing situation, in which the glow illumination turns into a blue-white colored light over the negative electrode and begins producing rapid degradation of the lamp.

Hence, for you to illuminate a neon lamp efficiently, you must have sufficient voltage for the lamp to "fire," and, and then, ample series resistance in the circuit to be able to restrict the current to a level that will guarantee that the lamp stays running within the typical glowing section.

Since the neon resistance by itself is extremely small soon after it is fired, it needs a series resistor wit one of it supply lines, called a ballast resistor.

Neon Breakdown Voltage

Commonly the firing, or breakdown, voltage of a neon lamp could be anywhere between approximately 60 to 100 volts (or occasionally even greater). The continuous current rating is fairly minimal, generally between 0.1 and 10 milliamps.

The series resistor value is determined in accordance with the input supply voltage across which the neon may be attached to.

When it comes to neon lamps being controlled with a 220 volt (mains) supply, a 220 k resistor is usually a good value.

With regards to many commercial neon bulbs, the resistor could possibly be included in the body of the construction.

Without any precise info given, it may be supposed that a neon lamp may have simply no resistance while it is illuminated, but may have a drop of around 80 volts across its terminals.

How to Calculate Neon Resistor

A proper value for the neon ballast resistor could be determined by taking this benchmark into account, which is relevant to the precise supply voltage utilized across it, and presuming a "safe" current of, approximately 0.2 milliamps, as an example.

For 220 volt supply, resistor may have to lose 250 - 80 = 170 volts. Current through series resistor and neon bulb will be 0.2 mA. Therefore we can use the following Ohm's law formula for calculating the appropriate series resistor for the neon:

R = V/I = 170 / 0.0002 = 850,000 ohms or 850 k

This resistor value would be safe with the majority of commercial neon lamps. When the neon glow is not quite dazzling, the ballast resistor value could be reduced to drive the lamp higher across the typical glow range.

That said, the resistance must in no way be lowered too much which may cause the whole negative electrode to be engulfed by the hot glow, because this may indicate that the lamp is now inundated and getting close to the arcing mode.

One more issue regarding the power of the neon glow is that it may typically look a lot shiny in ambient light compared to in darkness.

Actually, in total darkness the illumination could be inconsistent and/or call for an increased breakdown voltage to initiate the lamp.

Some neons possess a tiny hint of radioactive gas mixed with the inert gas to promote ionization, in that case this kind of effect may not be visible.

Simple Neon Bulb Circuits

In the above discussion we have elaborately understood the working and characteristic of this lamp. Now we will have some fun with these devices and learn how to build some simple neon lamp circuits for using in various decorative light effect applications.

Neon Lamp as a Constant Voltage Source

Due to the neon lamp's constant voltage features under standard light conditions, it could be applied as a voltage stabilizing unit.

Neon Lamp as a Constant Voltage Source

Therefore, in the circuit displayed above, the output extracted from each side of the lamp might work like an origin of constant voltage, provided that the neon continues to work within the typical glowing region.

This voltage would be then identical to the minimal breakdown voltage of the lamp.

Neon Lamp Flasher Circuit

Using a neon lamp like a light flasher in a relaxation oscillator circuit can be seen in the image below.

simple neon bulb flasher circuit

This includes a resistor (R) and capacitor (C) attached in series to a supply voltage of a dc voltage. A neon lamp is attached in parallel with the capacitor. This neon is applied as a visual indicator to show the functioning of the circuit.

The lamp almost performs like an open circuit until its firing voltage is reached, when it instantly switches current through it quite like a low value resistor and begins glowing.

The voltage supply for this current source therefore needs to be higher than that of the neon's breakdown voltage.

When this circuit is powered, the capacitor begins accumulating a charge with a rate determined by the resistor/capacitor RC time constant. The neon bulb gets a voltage supply equivalent to the charge developed across the capacitor terminals.

As soon as this voltage reaches the breakdown voltage of the lamp, it switches on and forces the capacitor to discharge via the gas inside the neon bulb, resulting in the neon to glow.

When the capacitor discharges fully, it inhibits any further current to pass through the lamp and thus it shuts down again until the capacitor has gathered another level charge equal to the firing voltage of the neon, and the cycle now keeps repeating.

Put simply, the neon lamp now keeps flashing or blinking at a frequency as decided by the values of the time constant components R and C.

Relaxation Oscillator

variable flasher neon bulb

A modification in this design is indicated in the above diagram, by using a 1 megohm potentiometer working like a ballast resistor and a couple of 45 volt or four 22.5 volt dry batteries as the voltage input source.

The potentiometer is fine-tuned until the lamp illuminates. The pot is then rotated in the opposite direction until the neon glow merely fades out.

Allowing the potentiometer to be in this position, the neon must then begin blinking at different flashing rates as determined by the value of the selected capacitor.

Considering the values of the R and C in the diagram, the time constant for the circuit may be evaluated as follows:

T = 5 (megohms) x 0.1 (microfarads) = 0.5 seconds.

This is not specifically the true flashing rate of the neon lamp. It might require a period of several time constant (or fewer) for the capacitor voltage to accumulate upto the neon firing voltage.

This may be higher in case the turn-on voltage is over 63 % of the supply voltage; and may be smaller if the neon firing voltage spec is lower than 63 % of the supply voltage.

Additionally, it signifies that the blinking rate could be modified by changing the R or C component values, possibly by replacing various values worked out to provide an alternative time constant; or using a parallel attached resistor or capacitor.

Hooking up an identical resistor parallel with R, for instance, would likely make the flashing rate two times more (since adding similar resistors in parallel causes the total resistance to be reduced to half).

Attaching an identical value capacitor in parallel with the existing C would likely cause the flashing rate to become 50% slower. This type of circuit is referred to as a relaxation oscillator.

Random Multiple Neon Flasher

Replacing R with a variable resistor could enable adjustment for any specific desired flashing rate. This could also be further enhanced like a novelty light system by attaching an array of capacitor neon circuits, each having its own neon lamp in cascade as shown below.

neon bulbs random flasher circuit

Each of these RC network will enable a unique time constant. This may generate a random flashing of the neon across the entire circuit.

Neon Lamp Tone Generator

Another variation of a neon lamp application as an oscillator could be a relaxation oscillator circuit is shown in the figure below.

This can be a genuine signal generator circuit, whose output could be listened through headphones or perhaps a small loudspeaker, by suitably adjusting the variable tone potentiometer.

Neon flashers could be designed to function with random manner or sequentially. A sequential flasher circuit is displayed in Fig. 10-6.

Sequential flasher using NE -2 miniature neon lamps

Additional stages could be included in this circuit, if required, by using the C3 connection to the very last stage.

Astable Neon Lamp Flasher

Lastly, an astable multivibrator circuit is revealed in the figure below, employing a pair of neon lamps.

Astable multivibrator circuit, each neon flashing alternately

These neons will blink or flash on/off in sequence at a frequency decided by R1 and R2 (whose values must be identical) and C1.

As a basic instructions on flasher timing, increasing the ballast resistor value or the capacitor value in the relaxation oscillator circuit can reduce the flashing rate or the flashing frequency; and vice versa.

However, in order to protect the working life of a typical neon lamp, the ballast resistor value utilized must not be lower than approximately 100 k; and finest results in very simple relaxation oscillator circuits may often be accomplished by maintaining the capacitor value under 1 microfarad.

More Assorted Neon Circuits

Neon Twinkling Star

The next neon lamp circuit provides a lovely neon glitter shine light outcome. In the past, I employed this design oftentimes for party decorations. Because of the dissimilarities in lamp firing limits, the illumination sequence results in essentially random therefore twinkling lights or "tiny blinking stars."

At any moment, a single (or sometimes a couple of) lamps tend to be illuminated allowing the capacitors their charging routes. When the capacitors charge, this exceeds the firing threshold for another neon, forcing it trigger ON. Due to a commutation impact, some lamp in the lit up mode subsequently turn off some other lamp which are previously lit up. These RC and neon networks are basically relaxation oscillators.

For these oscillators to work, the resistors and supply voltage all need to be selected to sit around the negative resistance portion of the NE-2 neon curve. This often takes place within a somewhat large value range. Some further experimentation might be required for something additionally extravagant.

Resistors having the value in the range of one to four megohm can be generally a good place to start. Precisely what is amazing is the fact that I still have no idea how to implement this kind of illumination pattern using LEDs which could turn out to be distantly as easy, as inexpensive, or as low in energy consumption.

Neon Lamp Driver Circuit

 With a 5- to 15-volt DC supply, the circuit above may be used either to drive a neon light or for generating a low-current DC voltage of up to many hundred volts. The 555 is set up as a 3-kHz astable multivibrator, with its square-wave output supplied to the primary winding of the indicated transformer T1, via the resistor R3.

Transformer Details

T1 in this circuit can be a tiny audio transformer with appropriate turns ratio required to produce the necessary high output voltage. A 10 volt input supply and a transformer having a 1:20 turns ratio will provide an unloaded DC output of 200 volts peak in this circuit. With the help of  a half-wave rectifier and a filter capacitor, this AC power may be readily converted to DC.

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About Swagatam

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials.
If you have any circuit related query, you may interact through comments, I'll be most happy to help!

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  1. Abdul says

    Great, useful

    Reply
    • Swagatam says

      Thanks for the feedback!

      Reply
      • David says

        Very good info in your article. Similar to SStark, I am EE and played with neon lamps in the 60s. Three comments.
        1. When neon lamps hooked to ac, both electrodes glow. Only need resistor on 1 leg.
        2. Even with isolation transformer, there is still high voltage. So experimenters must be careful!
        3. Having fuse is a very good idea. Best to employ a fuse of a 10 mA (milli-amps). Choose 125 or 250 voltage rating, as appropriate for the application.

        Reply
        • Swagatam says

          Thank you for the valuable information. Much appreciated!

          Reply
  2. Ali Khayri says

    Dear Swagatam,
    Thanks a lot for these information, but I have a comment on “Neon lamps only working on DC”
    In practice I have many circuits that works on AC the simplest is the Screw driver voltage tester.

    Reply
    • Swagatam says

      Thanks Ali, neon bulb will also work with high voltage DC as suggested in the above article.

      Reply
      • SStark says

        Not getting critical here but … I to am an Electronics Engineer (40 Plus Years). I used to play with neon bulbs when I was a kid in the 60’s. Radio B batteries were to expensive so we just used a cast off power cord and AC line voltage to build our creations. Neon Bulbs will work with either AC or DC. That’s the wonderful thing about them, it does not really matter. With that said I agree with you approach here… the novice experimenters probably should not be connecting up to AC line voltage with out an isolation Transformer or at minimum a fuse. Keep up the good work.

        Reply
        • Swagatam says

          Thank you very much for your kind feedback!

          Reply
  3. Kumar says

    I have seen green neon bulbs in Geisers. What might be the gas inside? Where can we get different colour neon(Tiny) Indicators

    Reply
    • Swagatam says

      Sorry i have no idea about it.

      Reply
    • Phil Landmeier says

      I believe I can answer this one. Years ago there was a wide variety of gas discharge lamps and in different sizes. Neon was just one. Another common version was filled with argon and glows purple. Argon is the better choice if you want to use a gas discharge lamp as a voltage regulator. A neon bulb will also regulate, just not quite as well as argon. It’s hard to find these things now because it’s all been replaced by LEDs and solid state.

      If I’m not mistaken, the green neon bulbs you saw looked like they had a white coating on the inside, yes?. That’s a phosphor that glows green when excited by UV light. In addition to the pinkish orange color we associate with neon, ionized neon emits light far into the UV range. This UV light excites a phosphor on the inside of the lamp. There’s no danger because the glass of the lamp envelope absorbs nearly all the UV. The lamp may also have been filled with argon instead of neon. But the green light comes from the glow of the phosphor, not the gas.

      Best regards,
      Phil

      Reply
      • Atef says

        💞

        Reply
  4. ULHAS SAWANT says

    Very Good Tutorial on Neon Lamp

    Reply
  5. Edward says

    i became interested in gaining knowledge with your projects. I wish all your endeavors wold be successful and that would help the people at large.

    Reply
    • SM says

      Thank you Edward, I appreciate your thoughts.

      Reply
  6. Jesús Fernández de Velasco says

    I was looking for that information a very long time ago, thanks God I’ve found your site and let me tell you this… SOOOOO COOOOOOL! Thank you very much!

    Reply
    • Swagatam says

      You are welcome!

      Reply
  7. s.sathananthan. says

    Sir, now I am clear that neon led doesn’t have polarity in strict sense but I have a rice cooker with three functions with three neon led indicators. The circuit has connections for diodes in series with one terminal of the bulb and other terminal is in series with a resistor. The cooker is powered with AC. I wish to know that in this circuit the leds are working in DC and not AC. Please answer.

    Reply
    • Swagatam says

      s.sathananthan, the LED is working with half wave DC!

      Reply
      • s.sathananthan. says

        Thanks a lot for the information that clears my question well.

        Reply
        • Swagatam says

          You are welcome!!

          Reply
  8. Phil Landmeier says

    Hello Swagatam. I’m glad to see people still playing with neon lamps. They’re a great learning tool that’s fun. In addition to blinkers, chasers, flip-flops (toggle and S/R), etc. they are great for playing with static electricity, detecting RF fields, even displaying when the atmospheric voltage gradient is high enough to light them up.

    Anyway, I had one comment about your Random Multiple Neon Flasher schematic. Notice that C1, C2, and C3 are connected in parallel. 😉 There’s only one capacitor needed for this circuit, which I once built 60 years ago. Lol. I made mine with one R, one C, and six neons connected in parallel. You get a wild chaotic action that’s extremely sensitive to ambient light. It performs best in total darkness and with the six bulbs located close enough together that their emitted light affects adjacent bulbs. In bright light, the action drops way down and almost stops.

    Best regards,
    Phil

    Reply
    • Swagatam says

      Thank you Phil, for your valuable feedback, hope the readers will find them useful.

      Reply
  9. Mike Fox says

    Can we make a 120vac neon panel lamp flash at about 60 IPM with just a resistor and capacitor?

    Reply
    • Swagatam says

      that maybe possible by selecting the RC network appropriately…

      Reply
  10. Harry says

    A DUMB FARMERS QUESTION;
    I have an electrified cattle fence. Puts out about 5000 volts in short pulses.
    How can I ballast a miniature neon bulb so I can install a permanent indicator that the fence is functional and getting its power? I will install several of these at various sections of the fences.
    A simple circuit diagram please…..
    Thanx for any possible help..

    Reply
    • Swagatam says

      You can probably try connecting 3nos of 330k in series with each terminal of the neon and connect them across the supply wires. If the resistors show burning tendency, you can connect more such resistors in series and check the response!

      Reply
  11. Paul Hess says

    I made the Neon Lamp Driver Circuit using a 120v to 9v AC adaptor. The turns ratio is about 13:1 with primary and secondary hooked up in reverse to make it a step up transformer and I used a 12v battery. I was only able to make it work by connecting R1 across pin 7 and the voltage supply. I found this out on accident.

    Reply
    • Swagatam says

      The transformer here is an audio transformer which has a very high number of turns for the secondary winding…R1 should be exactly where it is shown since the configuration is a standard astable circuit design….nevertheless if the modification is working for you then three’s no problem in keeping it.

      Reply
      • Paul Hess says

        Could you recommend a transformer to use that I might find online? Thank you.

        Reply
        • Swagatam says

          If you search it online you may find many reliable sources, according to me.

          Reply
  12. Jeff H. says

    Jeff H. asks: I would like to (re)create a basic 80 volt sawtooth relaxation oscillator, like the above “more assorted” one, fig.A, where the neon lamp would simply be replaced by some other type of 11-18 volt driven component, in order to steadily drive an automotive ignition coil. Any thoughts? Thanks in advance.

    Reply
    • Swagatam says

      If you replace the neon with any other load, the oscillations would stop. It is the neon which is actually causing the oscillations.

      Reply
      • JeffH says

        Thanks for answering. But isn’t there a solid state device, such as a reverse biased diode or x-sistor, that can function and exhibit the same characteristics of the neon lamp, but at a lower 11-18 volts???

        Reply
        • Swagatam says

          You can use a diac, however the firing voltage of a diac is normally around 30V. Nevertheless, the capacitor value could be adjusted accordingly to get the desired frequency output

          Reply
  13. Bob says

    Just replaced T9 9 in fluorescent ceiling fan bulb with an 8 in non dim led. The ceiling fan and light are remote controlled so it is running off one switch on the wall. When the fan is on and light is off (via remote control) the LED has a little voltage on it and therefore it glows. Is it possible to use a neon indicator to absorb this voltage so the LED doesn’t light up?
    If so, would it be connected in series with the bulb in line with the line or neutral wire…or would it be in parallel with the LED bulb and connected to the same 2 wire nuts as the LED bulb.

    Reply
    • Swagatam says

      It should be connected in parallel to the LED, however I am not sure if the neon bulb would be able to absorb the residual voltage, but it is definitely worth trying. Another option could to attach a 0.1uF/400V capacitor parallel to the LED leads, this might also help to neutralize the LED glow while it is turned OFF.

      Reply
      • Bob says

        Thanks for the quick response; not sure this thread would still have life, haha. Gonna try the neon indicator. Will let you know how it turns out. Thanks again!

        Reply
        • Swagatam says

          Sure, no problem.

          Reply
  14. Terry says

    I have a similar issue, installed LED ceiling fixture on three -way switch.
    When the light is off half of the 12 LED chips are faintly lit.
    Saw somewhere on the Web that Neon indicator could absorb the residual voltage.

    Reply
    • Terry says

      Fixed my problem . Wired small light bulb pigtail with bulb in parallel with LED
      fixture. The small light bulb does not light but keeps LED lights
      from coming on when the 3-switches are off. When one of the 3-switches
      is on , both the LED and the pigtail bulb are lit. But the pigtail is
      inside fixture , cannot see it from outside fixture. Not a great solution.

      Reply

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