So apparently the only difference between standard bi-pin lamps and single pin “slimline” lamps is just the bases on the end. They aren’t HO or VHO, they are just instant-start only versions of the “normal” lamps.

Why would they feel the need to make an entirely new fluorescent tube base (adding ambiguity) when there literally is no difference between them and standard bi-pin lamps? Is it a durability thing? As far as I am aware, everything you can do with a single-pin (mono-pin?) lamp you can also do with a bi-pin lamp.

Just… why?

So apparently the only difference between standard bi-pin lamps and single pin “slimline” lamps is just the bases on the end. They aren’t HO or VHO, they are just instant-start only versions of the “normal” lamps.

Why would they feel the need to make an entirely new fluorescent tube base (adding ambiguity) when there literally is no difference between them and standard bi-pin lamps? Is it a durability thing? As far as I am aware, everything you can do with a single-pin (mono-pin?) lamp you can also do with a bi-pin lamp.

Just… why?

instant-start lamps generally have more robust cathodes designed for instant-starting (well as best as you can, it will always be damaging to a hot cathode) the most prime example is the special cathodes you find in SOX lamps for example, while you can instant start a bi-pin lamp, but its not good for it, (even a F40T12/IS tube the rare instant-start *bi-pin* version of the F40T12 has the pins shunted together internally on each end)

r17d bases where introduced for electrical safety reasons, to lessen the chance of getting a shock from the tube if your holding one end of it while inserting the other end into a live fixture (and I certainly remember shocking myself doing that with an F20T12 when I was young LOL)


Never seen a single pin T5 tube mind, but there is the single pin F42T6 and F64T6, T6 series of slimline tubes

Ease of handling I bet.

In Europe, the use of single pin lamps is very minor, and AFAIK limited to explosion proof luminaires for mine lighting.


 

instant-start lamps generally have more robust cathodes designed for instant-starting (well as best as you can, it will always be damaging to a hot cathode) the most prime example is the special cathodes you find in SOX lamps for example, while you can instant start a bi-pin lamp, but its not good for it, (even a F40T12/IS tube the rare instant-start *bi-pin* version of the F40T12 has the pins shunted together internally on each end)

I guess if you don't have to worry about a preheat voltage on the cathodes, then you can have a little more design freedom because if the filament does end up shorting out, it doesn't actually matter. Do they actually make instant-start fluorescent tubes with beehive cathodes like SOX?

r17d bases where introduced for electrical safety reasons, to lessen the chance of getting a shock from the tube if your holding one end of it while inserting the other end into a live fixture (and I certainly remember shocking myself doing that with an F20T12 when I was young LOL)

Isn't r17d only for HO and VHO tubes? Also, if you are holding a lamp by the pins (especially when installing it), I think that is just some Charles Darwin action (no offense). I guess you were young so that's okay lol.

They are Ultra Rare here in Europe, except for explosion proof lights indeed. Philips makes 40W cold white 640 colour tubes called TL-X, which are still in service in some lamps at my work actually! A lot of those old fixtures are still in service and still getting relamped to this day! and they recently bought a whole box of new such tubes, so they seem to still be available. They have an ignition strip to help them strike. I’m unsure how the ballast arrangement looks like inside those fixtures, so I’m unsure if they strike on just mains voltage 230 volts alone or if there’s some auto transformer ballast or something else. The fixtures I believe are made by Stahl, unsure about the model.

  U have keep in mind the instant start lamp came out first before HO and VHO.  They did single in slimeline 6 and  8 footer first cause there easier to install long lamp usimg
 The spring  loaded socket and stationary socket.  Imagine
 Taking a  8 foot bi pin lamp and  rotating it at both end
 And making sure both pins are in.  It would end up with a 3 man crew to change a light bulb!

Indeed, hehe.    It is hard enough to get a 5 foot bulb to seat correctly into their bi-pin sockets sometimes, haha  

There are very good reasons why the single-pin Fa8 and then Fa6 bases were developed!  Along with entirely different electrode structures.

When the first instant start circuits were developed in the USA, to strike regular preheat / switch-start tubes by applying a high open circuit voltage directly across the tube, a number of problems arose.  Firstly and perhaps most obvious was the drastic reduction in life.  At room temperature the emissive coating on the electrodes only emits about 25 electrons per second, and to raise that to the level required to carry the then typical T12 tube current of 430mA caused an extremely sudden thermal shock.  The emitter coating surface reaches its full operating temperature within only about 1-2 mains cycles, which corresponds to a heating rate of about 100,000°C per second!  That explosive violence knocks out large chunks of emitter material, of course leading to a very sharp reduction in life.  That problem was at least partially overcome with GE's invention of the triple coiled electrode structure in 1941, in which a basket wire runs through the centre of the coils in an attempt to better hold on to to the emitter, and enable a much greater pick-up weight, to provide a greater supply and longer life.

The second problem was that these instant-start circuits began killing people.  If an installer is unlucky enough to be holding the pins at one end of the tube while inserting the other into a live socket, the high OCV of the autotransformer ballast causes instant breakdown of the gas filling and the current flows through the operator to ground, with potentially fatal consequences.  Or at least to create surprise and cause them to fall from a ladder.  The quick and dirty solution was to short-circuit the pins inside the cap, and run a wire from one pin of one lampholder to one pin at the opposite end, and use that to complete a circuit that powered up the ballast.  It was not possible for the high voltage to be applied to either lampholder until both ends of the tube had been installed, thereby eliminating the risk of electrocution.

Next another problem was detected, if these /IS tubes with shorted pins were accidentally installed into circuits for regular switch-start tubes, or the early trigger-start circuits that were beginning to emerge (similar to what is known as Quick Start in the UK).  Those were the predecessors of GE's Rapid Start invention of 1952 in which the cathodes are continually heated to provide faster and more reliable starting, and approximately doubled tube life along with a slight increase in discharge efficiency due to the lower discharge volt drop.  Incidentally those /RS lamps were also technically different, having 3.6V triple coil cathodes vs the regular 8-10V coiled coil of preheat / switch-start so as to reduce power losses in the tube ends - but also with three other distinct reasons.  Anyway, the problem was that the /IS tubes caused severe overheating of the ballasts, with consequent risk of fire.  Lampmakers were urged to stop putting more of these potentially dangerous tubes with shorted pins on the market and to develop a better solution.

The result was the Fa8 cap with single short fat pin at each end, first introduced along with the Slimline tubes of 1944.  The pin was made fat enough that inside the lampholders, there were two separate spring terminals that made contact with both sides of the lamp pins.  One of those terminals at each end was wired up as before, to avoid electrocutions by switching on the power to the ballast only once both lampholders had been inserted (I think in some later designs the double-contact lampholder was used only at one end, after the invention of the plunger-type lampholders with one depressable end and one fixed end.  That required that the customer first install the tube into the socket with plunger, depress it, and then the lamp could spring back into the opposite end's fixed lampholder.  The two contacts were then only required in the fixed lampholder, which could be connected in series with the mains supply to the transformer primary. 

The original Slimline T4, T6 and T8 5.5ft and 7.5ft lamps of 1944 as well as the extended T12 range of 1947 were first introduced for operation only on 120mA and 200mA, which is rather low.  But that was back in the days when GE and Westinghouse were still doing everything possible to limit the use of FL lamps in high lumen industrial applications so as to protect their power generation businesses from declining electricity demand - they still wanted customers to buy big high wattage incandescents for such uses.  Due to the low tube current, the cathodes for Slimline had to be a different design than regular Preheat tubes.  Later, Sylvania was pushing very hard the concept of higher lumen tubes for industrial lighting, same as it learned from the British situation of highly loaded industrial tubes, via its associations with Thorn Lighting.  Sylvania also had no conflict of interest in the power generation business - until 1956 when it became the world's first nuclear fuels manufacturer.  But before that it pushed the Slimline tubes up to 300mA and then the cathode designs had to be changed again to permit operation across a very wide range of different currents - today's Slimline tubes are happy at either 120, 200 or 300mA.

An unexpected early spinoff application of Slimline tubes was in the mining industry, and in areas with explosive atmospheres.  Regular fluorescent systems had the drawback of causing occasional explosions due to the poor contact between lamp pins and lampholders, which resulted in tiny arcs, but the high open circuit voltage of Slimline systems significantly reduced that risk, although not completely.  Some additional improvement was needed.  Flames cannot travel through small channels or capillaries due to the well-known quenching effect (which explains why the flames of a typical gas burner don't disappear back through its holes and cause combustion in the gas pipes).  It was attempted it was tried to enclose the Fa8 base pins in a close-fitting tubular hole within the lampholders, but the tolerances did not allow a true explosion-proof design.  It was necessary to make the pins much longer so that the lampholder contacts could be recessed more deeply.  The diameter was also reduced so as to reduce the effective width of the annular channel around the pin's circumference.  This resulted in the Fa6 lamp caps with long short pins, which are still sold today by Philips as the TL-X type.

So there are actually good reasons for the design differences of Slimline tubes!  Unfortunately these details are not widely known or documented in many books or manufacturers brochures, and easy to be lost over time.

@LBF - The Swedish company Aurora did make Long T5 lamps with single pin bases.  I remember seeing them at one of the Frankfurt Light fairs, and not so long ago maybe around 2010.  They were proposed as a higher efficacy alternative to TL-X, but I do not think were successful.  The market is maybe too small and luminaire makers did not see the need to redesign their products for such an upgrade.

Very interesting read!! THank you for the insight into this I have always been curioss why single pin tubes were developed, and now I feel like I finally have some answers to that

 I was a civil service electrician working for a large New York City agency, the Dept. Of Social Services. There were two instances where I was given work orders to replace defective ballasts in different locations. Arriving at the locations I found that somehow the custodians had ordered and installed f40t12IS instant start lamps in rapid start fixtures. Interestingly, when the correct bulbs were installed, all the lamps lit. There seemed to be no damage to the ballasts even though the cathode heater windings had been shorted for an extended period.
One thing I have been curious about is the difference in the wiring between the lead lag ballasts and the later series sequence ballasts. The series sequence ballast wiring has the hot wire going to one circuit interrupting lamp holder,and the grounded neutral wire going to the other circuit interrupting lamp holder. But the lead lag ballast has the hot wire going directly to the ballast and the grounded neutral going to one circuit interrupting lamp holder, coming out of that lamp holder and going to the other circuit interupting lamp holder and then to the ballast. Why was this done?

There are two aspects the arrangements need to fulfill:
1) The interrupting connection needs to be on the lamp end that is connected to the mains input, so it may share contacts.
2)he ballast design aims to use the mains voltage as at least a part of the total OCV generation, so the transformer does not need to have that many turns to reach the required OCV. The reason is, less turns means shorter wire and that means lower losses, so if the total losses could be the same, it allows thinner wires, so generally smaller and cheaper assembly.

With series connected lamps the only way to meet the above requirements is for the mains to be "between the lamps" (and so the secondary winding is between the other ends). And so one lamp is disconnecting the Phase input and the second the Neutral.

With parallel connected lamp circuits the cold ends are connected to the Neutral, so both cutout contacts are there.

You may also create a 4-lamp ballast with two series lamp circuits. Then each circuit will have one lamp on the Phase input and one in the Neutral input, with the two secondaries (one likely with a series capacitor to form a lead-lag combination) between the "hot" ends of each lamp pair. But dunno if such ballasts really exist in real life, 4 large lamps on a single ballast may be a bit impractical and won't bring that much advantage (practically just 1 capacitor less per 4 lamps) over the drawbacks (4 cutout connections, so 4 places for the circuit to fail in a way to disable all 4 lamps at once)...

I think that the R17d or also called RCD is a more robust solution for PG lamps which are T17 (54mm) and up to close to 2400mm long! It can be painful to install a such thick tubes into fixtures when using a ladder in the highs! Especially when one have to re- lamp a couple dozen of these. I think that type of socket was firstly introduced to the PG tube and shortly later on the VHO/HO tubes were introduced?

The R17d caps were actually first introduced in 1952 with GE’s original HO series T12.  Then when the PG arrived in 1956, and the Sylvania VHO, both adopted the same cap design.

Interesting how well thought out the slimline systems were with the built in disconnect socket used to interrupt power to the ballast if a lamp is removed.

A similar disconnect was used on some types of single lamp residential LPF ballasts designed for F20 or F40 lamps. The ballast neutral would be run though the lampholder which was a disconnect type designed to break the neutral if a lamp pin wasn't present. The disconnect used only one pin on a standard bipin lamp instead of passing power through the electrodes so regular non shunted lamps can be used, just a special socket for that end. Oddly enough only LPF rapid start style ballasts ever had that feature, two lamp ballasts and HPF ballasts never required disconnect sockets.

I also never seen this system used for electronic instant start systems as well. Bi-pin T8 lamps did shunt the lamp pins but this was done using shunted sockets instead of special shunted lamps, which allowed the same lamp to be used for rapid start and programmed start ballasts as well. Installing a T12 electronic ballast into a existing magnetic slimline fixture typically required rewiring the fixture to bypass the AC disconnects used for the magnetic ballasts.