Hi All

Probably a silly question that there is a logical answer to...

Why did Slimlines not take the place of Bi-Pin fluorescents? From all reports they last longer and are more efficent than their bi-pin counterparts? The manufacturing process must surely be cheaper?

By the way I love slimlines and hope to own one at some stage.

Good question...I have no idea why there's the 2 different types.
Or why in the US 8-footers are single-pin/slimline, and overseas 8-footers are bi-pin (LOL I'd love to have one of those)

You might be able to find some of the shorter slimlines on eBay (like 2-footers) and have them shipped over to you

R U sure that single pin lamps have longer life than bi-pin lamps?
I think that this is just the opposite:
1. "Slimlines" aren't cold cathodes fluorescent lamps, but they still starts directly from the ballast OCV with cold cathodes, so this means that each start cause more stress on them than bi-pin lamps operating on rapidstart and preheat magnetic ballasts, and PTC, rapidstart or programmeed start electronic ballasts.

To be honest Dor, no - it's just an assumption I have that Slimlines have a longer life than Bi-Pins. I'm trying to find out why or if my assumption is even correct.

Xmaslights guy - thanks yes I have often pondered getting hold of one.

@Blake, Dor: The reason could be, than the slimlines have the electrode designed to suffer less on cold starts (as there is no preheating physically possible at all; typical is twisting the filament into beehive shape, what redirect the heavy ions to strike each other instead of the electrode surface).
Bi-pin lamp design could save the extra cost on assumption, than the electrode preheating reduce the stress on them, so they do not have to be so robust against sputtering (so saving the cost related to filament shaping).
As a consequence, the slimlines could last longer...

The Slimlines are rated LESS hours than bi-pin. At the radio station here, they are run 18 +   hours a day and turned on at sign on, and off at 6 PM when I leave.

So why with LPS lamps, each starting put stress on the electrodes (Which are shaped exacly like the slimlines [And the european single pin lamps that designed to operate without a starter on a preheat ballast]), and shorts their life if it is done many times?
And why energy saving CFLs haven't behave shaped electrodes, if they are always instant started?

The official rating take into account certain switching pattern (usually ~3 hours ON/15 minutes OFF), what mean per 1000 rated hours it would encounter given amount of cycles as well. For
That pattern would yield for the cold started lamps way shorter life rating, than for lamps rated for certain amount of preheat from the reference ballast. There, the cold started lamp life is not limited by the the burned hours, but more by the number of starts.
Now if you turn the lamp ON for 18hours, it means your lamps encounter 6x less switching cycles per the same burning hours, compare to the reference pattern used for lamp rating.

Now if you have two lamp systems, where on reference setup one degrade only by burned hours (e.g. programmed start) and second mainly by switching cycles (e.g. the slimlines), the first one would stay on the same burned hours life even in your application, but the life of the second system would be up to 6x longer when measured on burned hours (assume hypothetical lamp aging only by number of starts).

In real life the 18hours/start would make the "burned hours" a dominant factor even for cold started lamp, but their life would be easily 2..3x longer than with the reference pattern, so they could easily outperform the preheated system on the real lamp life.

Very related is the reason, why (good quality) electronic instant start ballast could yield longer life than preheat or RS magnetic on installations with long hours/start, as the low frequency feed of the magnetic ballast cause faster electrode wear during steady run time than the high frequency of the electronic one. So when the extra starting wear become insignificant (on systems with >6..8 hours/start), the more gentle drive of the IS ballast could really yield longer lamp life.
But that would bring real advantage only if the electronic ballasts alone would be reliable enough...

So why with LPS lamps, each starting put stress on the electrodes (Which are shaped exacly like the slimlines [And the european single pin lamps that designed to operate without a starter on a preheat ballast]), and shorts their life if it is done many times?

The beehive filament shape help to reduce the wear, but it is by far not able to completely eliminate it. It is only the best known shape, by far not an ideal one...

And why energy saving CFLs haven't behave shaped electrodes, if they are always instant started?

Two aspects:
- Compare to lamps relying purely on the glow discharge to heat up their electrodes, CFL electrodes get ~80% of their cathode heating from the external circuit, so even when instant started, the cold cathode stress is ~5x lower than the pure glow heated lamps (SOX, slimlines,...). Therefore the electrode shaping would not bring as much an advantage as it bring with the SOX(,...).
- Shaping the filament is not for free in the mass production and CFL's are designed to be cheap in the first place.

And by the way it is not 100% true the CFL's using straight filament: The filament spring is usually "double-coiled" (about 2..3 turns), what is a kind of compromise: Not as expensive as the beehive filament of SOX, but still providing some means of sputter protection compare to straight filament. But the main driving force there was to fit the filament inside the narrow tube without colliding with the walls during manufacture...

Thanks all for these interesting points of view. It is rather intriguing - There are two points of discussion - life span and efficiency. I like how the slimlines install so easily into the sockets. I'd like to know the timelines - which came first? Slimline or bi-pin?

I think the seemingly long life of slimlines comes from their typical use, where they run long hours per start, often only being started once per day.  As far as I know, they use the same electrode design as standard bipin lamps.

As far as which came first, single pin tubes, modeled after lumalines with cup terminals and single-ended electrodes where developed and tested early on, but they were difficult to manufacture and required more complex ballasts.  Bipins were developed as being easier to manufacture and using simpler ballasts.

I've watched the slimline tubes EOL and the cathode / filaments are the same as on bi-pin lamps.  The EOL can come to an abrupt end when a red filament gets flung off so hard it hits the glass and cracks it. HSSSSSSSSSSSSSSSSSSSS and lamp goes out.

I have yet to witness a loss of vacuum EOL in person. This is because I am anxious about the possibility of catastrophic failure where the tube suddenly shatters. Which reminds me - I gave Al such a tube to finish off in my absence - I wonder if he's done it? hmmm..

You can see electrodes design by lasershading.