This is an American point. Elsewhere in the world, T8 36W is equivalent to T12 40W. Also to large PL-L 36W CFLs. And freely interchangeable except when used on rapid-start, which mostly died out at about ~1980s.

The same goes to rare T10 tubes.

I'm not Sure if anyone has the same type as me, but as of the other side I'm pretty much a techno house guy. Nothing than that other type usually does not sound too good for my ears. The Remover one is pretty a good one, which is by Carlo 

Original argon T12 tubes weren't efficient enough to satisfy these greedy people apparently . So alternatives were made. But some are confusing, and I have some questions. Here we go:

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1) 48T12 40W -> 34W Conversion:
Lamps fitting the typical 48T12 dimensions of a 40W lamp that only use 34W exist. I have certainly burned through a few in my life. It is my understanding that they are filled with a little bit of krypton among the normal argon to make their running voltage lower. This also has the unintended effect of making their striking voltage higher. Is this correct? I sometimes hear people have trouble running these, what ballasts are these suitable for?

2) T12 -> T8:
On Lamptech, I can't tell whether is it implied that krypton T8 lamps were meant to be retrofits for T12 lamps. In my calculations (admittedly flawed), running a 48" F32T8 lamp on a 48" F40T12 ballast would result in a little less than 400mA instead of the necessary ~217mA. And I know that different ballasts exist for both types of lamps, so they are likely not compatible. Were these ever supposed to be retrofits? Why couldn't they be made to be retrofits for T12s?

3) T12 -> T10:
I hear of these Japanese T10 retrofit lamps that are T10 diameter. How do they compare to the T12 Supersaver-style retrofits? Why didn't they catch on much over here?

4) Other technologies:
Is there anything I am missing? Did other countries or companies have other more interesting advancements in retrofit fluorescent lamps?

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Thanks!

@joseph_125
Very interesting, I have heard of powertwist but somehow never noticed they were T9. Very interesting compatibility.

@LightsAreBright27
I did not know that, I wonder why they chose T10 over other diameters. Another example of T9 which I am just hearing about now lol. Never heard of T11 either, very interesting.

@RRK
Ahh I see, so it is just easier to go all the way down to T8 than to remain somewhere in the middle.

Oh yeah, for fun and curiosity they have their place - i have a blue and a green CFL sitting around (as well as some decorative CCFL in yellow, pinkish-red etc).

But i mean, it would surprise me if enough people bought screw-in CFLs for general lighting purposes, to spend shelf space on in the 2020s.

There is some fun with colored CFL versions, green terbium ones are particularly interesting, as they also emit some sub-bands in yellow-red, can be thought as usual 3-phosphor spectrum 'dissected', as in normal lamp these overlap with red phosphor output.

That way, colored T4's are some fun with spectrometer too, especially if you get them at closeout price of fraction of $.
 Surprisingly, there is washed-out red (fluorogermanate) strong orange red (europium) and pinks (blue + fluorogermanate or europium).

CFLs, both self-ballasted and externally-ballasted varieties, are still widely available in the United States. You can run down to Home Depot or Lowe’s and pick them up.

Did anyone actually still buy them? I cannot think of any application where a CFL is preferred over LED.
Holding on to incandescent i could imagine for a while before LEDs got really good and affordable, but i don't think anyone laments the disappereance of CFLs. I got a few in my living room currently and they're 'just okay'.

I'm using Samsung Galaxy A34 5G smartphone.

Last month, Philips and its CFLi OEM, Yankon Lighting, stopped producing CFLi at the same time. China Customs also issued an announcement stating that the import and export of such products will be prohibited in 2026. As the existing stock depleting, it will become increasingly difficult to buy CFLs with built-in circuits from well-known brands domestically or from foreign countries. Apart from China, Japan and several other nearby countries have announced similar production halt regulations. I’m not sure which countries still sell them currently.

But no big cry, as integrated CFLs are 100% superseded with definitely better performing LED sources. May be regretted for some very niche applications like spectrometer calibration.  I believe, single NOS samples for collecting and such application will be around for decades anyway. I have a drawer full of specimens)

Why was T10 not used more? It is a very interesting size, I don't think I would be able to identify it in the wild. Anybody have some T10 examples they would like to share?

Seems that T10 was some transient between T12 and T8. Without optimized fill (pure Ar like for T12) there will be a disadvantage of poor efficiency due to increased current density, with optimized (krypton mix) - a temptation to go further to T8 for even increased savings on phosphor and glass.