Extend Defective Fluorescent Tube-Light Life





Introduction: Extend Defective Fluorescent Tube-Light Life

Lights Contest 2017

Runner Up in the
Lights Contest 2017

I present here a non-standard scheme to extend the life of defective Fluorescent Tube-Lights.

As I will explain in the next steps this method is based on study of the the basic fluorescent tube and its operation using the wire-wound-ballast and electronic-ballast.

The tube I modified six months back is still working indicating that the normal life of the fluorescent tube can be extended by 20 to 30%.

This scheme came to mind based on experiments conducted on the electronic-ballast designed by me: https://www.instructables.com/id/Electronic-ballas...

I found that while fluorescent tubes were originally designed for wire-wound-ballasts which needed active filaments at both ends for their operation, electronic-ballasts are capable of operating with only one filament. In this mode the electronic-ballast is operated outside specified electrical limits but appears to have sufficient design margin for continuous operation.

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All content provided here is for informational purposes only. I make no representations as to the accuracy or completeness of any information. I will not be liable for any errors or omissions in this information. I will not be liable for any losses, injuries, or damages from the use of this information.

Step 1: The Modification


1. The burnt-out/fused filament and blackened tube end

2. The filament resistance shows open (OL)

3. The normal filament shows 20-30 Ohms resistance

4. The copper wire to be used for shorting the terminals at the blackened end. One strand from multi-strand household wiring cable.

5. The terminals shorted out

6. The resistance is now Zero

Step 2: Theory 1 : Fluorescent Tubes With Wire-Wound-Ballasts

Fluorescent tube-lights were designed to operate with wire-wound-ballast chokes. A more efficient electronic-ballast is now commonly used with these tubes.

Looking at the figure the following is the sequence of operations leading to the start up of the tube:

1. When the AC-Mains is switched ON, the circuit is completed through the ballast, the starter and the two filaments. The starter which is a mini-glow tube starts burning and heats up a bi-metallic contact within the starter. This causes the contact to close and a starting current now flows through the ballast and filaments.

2. This starting current heats up the filaments and electrons are emitted from them. With the starter contact closed the glow subsides and the bi-metallic strip cools down. After a short delay the starter contact opens.

3. Sudden opening of the contact while a current is passing through the inductive-ballast causes a high voltage to be generated based on the inductance value L of the ballast and the rate of change in current di/dt.

4. This high voltage L x di/dt across the tube along with the electron-emission from the filaments ionizes the gas within the tube and a discharge is setup between both ends.

5. This discharge and the coating on the inner side of the tube creates the fluorescent glow.

6. At this time the inductive ballast limits the current flow through the tube to designed limits and the voltage across the tube is not sufficient to make the starter glow and the starter contact remains open.

With continuous use the filaments deteriorate and usually one filament burns-out/fuses and that end of the tube is blackened. A continuity test on the fused filament would show open-circuit while that on a good filament would show 20 to 30 Ohms.

Step 3: Theory 2 : Fluorescent Tubes With Electronic-Ballasts

The electronic-ballast is designed usually as a half-bridge resonant-converter: https://www.instructables.com/id/Electronic-ballast/

Looking at the figure:

1. The input AC Mains voltage is rectified using a bridge-rectifier

2. This voltage is fed to a half-bridge resonant-converter operating at a typical frequency of 60 kHz.

3. The output of the half-bridge is connected via an inductor (L1), one filament, a capacitor (C1), through the other filament to the center point of C2/C3.

4. When the AC Mains is switched ON a starting circuit immediately energizes the half-bridge converter and a high voltage is developed across C1 which is the same as across the two filaments.

5. The mechanism for Ionization and setting up of the discharge is quite different as it depends on the frequency, the high-voltage and to some extent on the emissions from the filaments.

6. After start up the current is limited by the impedance of the inductor L1 and the resistance of the filaments.

While experimenting with the electronic-ballast I found that the tube-light started up and worked when one filament was by-passed and it worked intermittently when both filaments were by-passed. As I was working with my own design it was possible to monitor the tube current, the input currents and the dissipation of the active components. The conclusion of these experiments was that the electronic-ballast was capable of driving a defective tube-light with one filament by-passed.

I was able to confirm this with a commercial electronic-ballast as presented in the video.

Step 4: Experimental Measurement Data

I made some initial measurements of the lamp current using a digital multi-meter. However, as the frequency of the AC waveforms is ~60 kHz these values are not reliable being outside the frequency-response range of the multi-meter.

After setting up an isolated AC Mains power supply using an isolation transformer I was able to take more accurate measurements using an Oscilloscope with a bandwidth of 15 MHz.

The oscilloscope probe is 10:1 and current measurements are taken across a 10 Ohm resistor.

The following is the summary:

  1. The oscillation frequency is ~ 62 kHz
  2. Under normal conditions the Voltage across the tube is 106 V and the current is 28 mA indicating a power of 29 Watts for this 36 Watt Fluorescent tube.
  3. The voltage across one of the filaments is 2.4 V and the dissipation would be 0.7 Watts at 24 mA.
  4. With one filament shorted the voltage across the tube is 159 V, the frequency is not so steady and the current is 42 mA indicating a power of 66 Watts.
  5. The current increase is 42/24 or 1.5 times
  6. The power increase is 66/29 or 2.2 times



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    will it not short circuit phase and neutral?

    As we are using an electronic ballast the Phase/Neutral do not come directly to the terminals of the fluorescent tube. In the circuit for the electronic ballast (my earlier instructable) you can see that the phase to neutral connection is rectified and fed to a half-bridge. The half-bridge output after a resonant inductor forms one output of the ballast. The other is the mid point of two capacitors connected in series between the rectifier positive and negative. So, we will not short the phase and neutral.

    I posted a day ago on this saying, Oh bother, just go buy a new bulb. I realize that it was probably not the right thing to say but I will explain why I did. I am one of the old guys that tinker. I have tinkered since I was a little kid and always will. I have over the years found that some things are just not worth all the trouble, this is one of them and it is nothing new. I did this years ago on two of my old fish tank lights and this might be the reason you need to do this just like I did. I didn't have the money to buy new ones at the time so I did this to the bulbs and they went on working but only for about a month and then they were finished. One thing about this is that when I did it back then they didn't work when I put the tube back in and turned it on, I found that it had to go in a certain way. Now what I am saying on this subject is if you have the money to buy a new one do so instead of doing this. Bulbs last for years, by the time you go through all the trouble of finding wire, stripping it, uncoiling a strand of the wire, wrapping it around the tube prongs putting it back in and having it not work then having to take it back out and flipping it around, putting it back in and trying it again, you could have went to the store and bought a new one and been finished for another few years. That's all I was saying, if your doing it just because you like to tinker, great go for it, have fun.

    I could have found wire, wrapped the terminals, and plugged a bulb back in un under two minutes. Where is this mythical store you are talking about shopping at?

    Good for you. What do you want, a first place ribbon for the fastest wire finder, wire stripper, terminal wrapper, bulb replacer in the world? I have no idea what you are talking about when you ask what this mythical store I shop at is. You can buy new bulbs at any hardware store, lighting store, pet shop, where ever.


    The mythical store you can get to in under two minutes, frisbrob.

    corner store

    Appreciate your views, I also wanted to explain the theory behind this hack.

    And MOST of us appreciate your Insight on this. I have seen more than my share of fluorescent tubes fail during my lifetime. Many times I see the black end of the tube like this. I had no idea that in some instances the tubes life can be extended with such a simple modification. Thank you for sharing and I will file this one away and give it a try the next time I see a tube fail in this manner. :)

    Instructables is not about saving money. It's about doing fun stuff that may or may not work or save any money.