I know that these exist, and I know that they have filaments that are just shorted together at the base. I have the following questions:

1) Names:
Is it slimline? HO? IDK what they are called. Let me know…

2) Type:
Obviously they are instant start, but are they all HO/VHO or are there some normal ones?

3) T5:
I swear I have seen single-pin t5 tubes, but now that I am looking I can’t find them. Was this a thing?

Thanks so much!

They got the name slimline because early in their development they were going to use T8 tubes.  It was decided that 8-foot T8 tubes would be too fragile, so they went with T12 instead.  Slimline branding may have been a GE only thing.

Slimlines are not HO or VHO.  Although the tubes are the same length, slimlines use single pins and are instant start.  HO/VHOs use recessed double-contacts and can be preheat, rapid start, or instant start.  The 24-, 36- and 48-inch slimlines are essentially the same wattage as their bipin counterparts, although sometimes labeled 1 watt off.  For example, an F48T12 maybe labeled as 39 or 40 watts.  F24T12 maybe labeled as 20 or 21 watts.

I've seen T5 single pin tubes too.  I think they were commonly used in display case lighting.

I have a single pin T5 germicidal with plastic endcaps.
 https://www.lighting-gallery.net/gallery/displayimage.php?album=8026&pos=21&pid=245458
It is 3ft in length, labeled as TUV 36 and 40w.

They got the name slimline because early in their development they were going to use T8 tubes.  It was decided that 8-foot T8 tubes would be too fragile, so they went with T12 instead.  Slimline branding may have been a GE only thing.

Slimlines are not HO or VHO.  Although the tubes are the same length, slimlines use single pins and are instant start.  HO/VHOs use recessed double-contacts and can be preheat, rapid start, or instant start.  The 24-, 36- and 48-inch slimlines are essentially the same wattage as their bipin counterparts, although sometimes labeled 1 watt off.  For example, an F48T12 maybe labeled as 39 or 40 watts.  F24T12 maybe labeled as 20 or 21 watts.

I've seen T5 single pin tubes too.  I think they were commonly used in display case lighting.

Ahh I see so they are just normal (“N.O.”?) tubes with different bases essentially.

I have a single pin T5 germicidal with plastic endcaps.
 https://www.lighting-gallery.net/gallery/displayimage.php?album=8026&pos=21&pid=245458
It is 3ft in length, labeled as TUV 36 and 40w.

Yes, I have seen these too on Ebay. I thought they might have had porcelain bases but I guess not.

I think the display case tubes may have actually been T6.

1) There are quite a few different types of single pin fluorescents

1a) Cold cathodes were the first, of course

1b) 1944 GE introduced the so-called Slimlines, with Fa8 caps having a single short fat pin.  It was a wartime development demanded by big industrial customers, to provide slightly higher lumen levels and approximately double the tube length, thereby halving the quantity of required fixtures and reducing usage of metals.  The originals were tubes of 5.5ft length in T4/T5, T6 and T8 operating at different and relatively low currents, and a longer 7.5ft T8 tube which was similarly underloaded by modern standards.  Because of the longer and thinner designs they were called Slimline, but in 1947 thanks to pressures from Sylvania to achieve higher lumen levels required for factory lighting, T12 types were added to the range and then the Slimline name kind of lost its relevance.

1c) 1965 the European tubes with R18s single fat pin caps were introduced.  Pretty similar to the USA Slimlines but with protective bakelite shrouds over the pins to prevent accidental contact and make the system safe without need for complex lampholder designs that did not apply high voltages until after both ends of the tube had been installed.  They also had an internal ignition stripe to facilitate starting at normal mains open circuit voltages, without need for expensive step-up transformers.  The inventor was Philips, type TL-S, but they were also produced briefly by some British lampmakers as type MCFB.  Often they were used together with a tungsten ballast lamp instead of a choke ballast.

1d) 1967 or thereabouts, the Fa6 types were introduced with a single long thin pin.  This was a spinoff of the Philips TL-S which was sold as type TL-X, but I suspect first developed by Osram of Germany which also produced them, along with Tungsram of Hungary and a few other smaller companies.  The application is specifically for explosion-proof and mine lighting, the pin and lampholder dimensions are optimised to reduce the risk of igniting an explosive atmosphere.


2) As far as I know all are low current tubes.  Nothing to do with the HO 800mA or VHO 1500mA concepts.  The Slimlines were all initially for 120/200mA, later also 300mA.  The TL-S and TL-X are standard 400mA tubes.  But all have very special cathode designs to withstand the shock of instant ignition.

3) Produced briefly by Auralight of Sweden, but I think no longer available.  Those had Fa6 caps for explosive atmospheres.  Many Germicidal types such as illustrated below are also offered with Fa8 caps.

I have had one for a few years now but never lit it!