As I understand it, some fluorescent tubes have an externally applied conductive stripe along the length of the tube to eliminate the need for a grounded metal reflector nearby the tube. If you had a fixture that needed these tubes, could you make your own with some 1/4” copper tape? This tape is super accessible, they say even the adhesive is conductive (not sure if that is true), but theoretically it should have the same effect.

Would this work? I don’t have any fixtures that need this, but I would like to experiment with ballasting tubes with a conductive stripe.

It should work as long as it stays attached to the tube.
The problem I see in the adhesive deteriorating under the rather high blue and UV (although the longer wavelength A and B, but still energetic enough to attack the polymers) causing it to deteriorate and the stripes to fall off.

Plus many HF ballast need the reflector grounded as an RF shield, so the fixture meets parasitic RF emission requirements. Without that the fixture may be disturbing radio communications (e.g. the time signal distribution which generally works on low end LW in the 50..150 kHz range) too much and so become technically illegal to operate.

@Medved
Thanks, I wasn’t planning on using an electronic ballast. If I do end up trying this out I will definitely keep an eye on the adhesive.

As I understand it, some fluorescent tubes have an externally applied conductive stripe along the length of the tube to eliminate the need for a grounded metal reflector nearby the tube. If you had a fixture that needed these tubes, could you make your own with some 1/4” copper tape? This tape is super accessible, they say even the adhesive is conductive (not sure if that is true), but theoretically it should have the same effect.

Would this work? I don’t have any fixtures that need this, but I would like to experiment with ballasting tubes with a conductive stripe.

yes you could indeed, in-fact sometimes they did just that with aluminium tape

https://www.lighting-gallery.net/gallery/displayimage.php?pos=-223848


the main problem is as Medved says, is adhesion and robustness of the stripe over the life time of the tube, which is why in most cases they go with a sintered copper stripe on the tube (and even then I have seen many old examples where bits of the stripe has flaked away etc)



it is worth noting however that there are 2 types of "striped" tube, there is the TL-A/MCFA type of striped tube, those tubes almost always have 9V cathodes, and the sripe is designed to be connected to earth/ground

and then there are TL-M/IRS type striped tubes, in these tubes, which are almost always have 3.6V rapid start cathodes, there is a high ohmic resistor that connects the stripe to one of the electrodes, to tickle the length of the tube with OCV of the ballast, in this regard the whole setup it works a lot like the starting probe of a mercury lamp and the stripe should explicitly not be grounded

@LightBulbFun
I could just connect a wire right to the stripe and see what works more reliably in this situation, maybe grounding is better, or maybe a resistor to an electrode is better.

Does anyone know what value resistor was used for the stripe TL-M tubes?

@LightBulbFun
I could just connect a wire right to the stripe and see what works more reliably in this situation, maybe grounding is better, or maybe a resistor to an electrode is better.

Does anyone know what value resistor was used for the stripe TL-M tubes?

About 2 Mega-ohms or so is what I have seen/measured on European lamps

https://www.lighting-gallery.net/gallery/displayimage.php?pos=-51154

https://www.lighting-gallery.net/gallery/displayimage.php?pos=-223984

my Japanese Panasonic FLR40 /M tubes https://www.lighting-gallery.net/gallery/displayimage.php?pos=-235775

measure about 1.2 meg ohm and my Thailand made for the European market TL-EM Circline tubes, one of em measure just under a megohm



so I would say somewhere in and about 1 to 2 megohm? just make sure you use resistors rated for the potentially few hundred volts that will be across them should the stripe be earthed (ie by someone touching it)

@LightBulbFun
That is super helpful, thanks! I know these tubes are typically used in 240V countries, but I will be trying this on an F14T12 (pretty short tube), so hopefully 120V is enough to help. But this is purely experimental so we shall see, I might try this with an F4T5 as well.

There is also a conductive epoxy and conductive lacquer, containing silver or copper particles. Used in specially PCB making and in auto repair. And there is a black conductive coating based on disperse graphite (aquadag). All of these will work as ignition aids.

@RRK

This is just a temporary test for now, so I don't really want to glue stuff to the tube.

Also – Is there an easy (low quantity) way to source aquadag? I am semi-into vacuum tube making and this would be cool to have.

@LightBulbFun
That is super helpful, thanks! I know these tubes are typically used in 240V countries, but I will be trying this on an F14T12 (pretty short tube), so hopefully 120V is enough to help. But this is purely experimental so we shall see, I might try this with an F4T5 as well.

it probably should work alright for an F14T12, in-fact many single lamp Trigger or Rapid-start F14T12-F20T12 ballasts only have an OCV of 155V or so to stop the tube instant-starting before the cathodes have heated up somewhat


not sure I have seen an F4T5 with a stripe on it, but I have a Thorn F8T5 with a stripe on it, its not often you see T5's with stripes but one place you did see em was in low voltage DC Automotive applications, mine came from a 24V Military "penthouse" light as they are known there where actually services back in the day that would stripe a tube for you/you could ask many of the British mfg's to stripe a batch of tubes for you for an extra fee etc

(and these would of all been MCFA tubes)

@RRK


Also – Is there an easy (low quantity) way to source aquadag? I am semi-into vacuum tube making and this would be cool to have.

Googling for "colloidal graphite" reveals a few links with the material offered for sale in small quantities.

@LightBulbFun
That is super helpful, thanks! I know these tubes are typically used in 240V countries, but I will be trying this on an F14T12 (pretty short tube), so hopefully 120V is enough to help. But this is purely experimental so we shall see, I might try this with an F4T5 as well.

The purpose of current limiting resistor in series with ignition stripe is for electrical safety - so the stripe will function even if connected directly to one of the electrodes.

Interestingly, the other opposite way to reduce ignition voltage is to repel all possible moisture from tube surface, making surface resistance a true infinity (or close). That is achieved by treatment by a strong hydrophobic agent like silicone or teflon.