Actually IIRC the T12 15W came after the T8! There was a reason but can't remember what? This was the case also with the 3'?

Really? Yet they're so rare in my 50+ years on this planet.

I know I was amazed as to why! I'll ask Eliot!

Considering that the first two fluorescent lamps to be marketed were the F15T8 18" and F30T8 36", the T12 15W indeed was a later addition. I do not know when it was introduced though, or the reason why. In the USA the F15T12 18W was more common. In Britain the F15T12 18" and F30T12 36" seem to have been unique to Thorn. These variants are listed in all of my Thorn catalogues over the period 1969-1980. They were delisted in the 1983 catalogue and thereafter but continued in production, I have one from 1992. In pre-1969 British literature I find it listed only in an Ekco catalogue of 1956. Ekco was already part of Thorn by then. I will look further in my literature this weekend and see if I can find out more about these strange T12 variants.

Thanks James, looking forward to more enlightenment. I've noticed how 18" and 36" T12 has been far more popular in USA than here.

Just to say, I have an endura and philips 3ft t12 lamps so it appears to be more than just BLI

i also have some new old stock endura T12 30's, but recon they are re branded thorns, and the crompton daylights in T12 again looking like re branded thorns

The etched on these are unusually weak for thorns?

looks like bird crap on the packets !

It would have been one of those situations where it took a while for anyone to notice the etching ink running out on the machine.

Phil the endura tubes do look very thorn same ends and all but the cathodes are much better and different! You can tell an endura by the ware marks after a few thousand hours!

I know that the T12 variants of the T8 Argon Line (the F14T12 F15T12 F30T12) all have a lower arc voltage and higher current then their T8 counter parts a F30T12 is 85V 0.45A but a F30T8 is 100V 0.35A for example. I also know that the T12 counter parts are easier to start. (an argon T8 can have issues striking on resistive and RS/QS gear) i think they are more common in the US due to the more common nature of Rapid start gear and going back to tungsten ballasted F14T12 fixtures in which a F14T8 wont strike hope this helps heh

so were the T12 15 watt tubes no longer made after about 1983 then? i had seen some as a child in an internally lit sign, when i tried to buy some they wee not available, took me years to find any, then found 2 boxes full in an old electrical shop, both thorn branded, one box it cool white the other the rarther rare colour of de-luxe warm white !