Can someone give more details about gas fillings in T5 fluorescent lamps?
I know that the classic 4, 6, 8, 13 W lamps have argon fill, but I'm not sure about others.

There are 11, 15 and 16 W lamps which have the same length as 6and 8 W lamps.
And T5 HE and HO. Is the only diffrence in the electrodes or do they have a different gas filling pressure or even a different gas like krypton?
I know that T8 16, 32 and 51 W 'Eco'(Philips name) or 'ES' (Osram name) have xenon as the buffer gas, so maybe energy saving T5 tubes also have something other than argon. Even T5 HE and HO comes in a more recent energy saving version, like Philips Master TL5 ECO 25, 50, 73 W.

I just had a chance to play with some nice old Osram's T5 HE's and HO's, original German and Italian. I used my spectrometer to capture spectra from cold lamps (mercury not yet fully evaporated) to get the idea of what buffer gas fill is. Based on near-IR signature I see, a dense cluster of IR lines, I can say the fill is pure Ar, no Xe or Kr added. About the same that I see for small T5's and CFLs too. I remember reading somewhere too that the fill gas for T5 tubes is just plain argon. Note that some lightweight inert gas with high ionization potential as Ne or He may slip in unnoticed by this method, as it is not preferentially excited in the mix, but I did not see Ne pattern even around cathodes, where it can show up.

I don't have access to any newer 'economy' T5 tubes, so can not tell for them.

See, old school T5 13W runs at the same current as modern T5 HE 14W (170 milliamps), is about the same size and is almost mutually electrically compatible.

 

But 14W T5 HE aren't designed to be operated on the magnetic ballasts of 13W T5.

@dor123 Thanks for sharing this really hard to find information

Officially, no. In practice I believe 14W HE will run on 13W magnetic just right, may be with just a minor lifetime penalty due to a higher current crest.

13W tubes run on 14W HE electronic ballast with a slight overdrive. IEC 60081 datasheet prescribes 150mA for 13W tube on HF, 14W ballast will run it at 170mA, but still within IEC 60081 spec (180mA max). Nice T5 HE programmed start electronic ballasts are so ubiquitous today, not much need to play with magnetics.

But 14W T5 HE aren't designed to be operated on the magnetic ballasts of 13W T5.

The topic is about gas fill, the magnetic ballast (aka low frequency operation) compatibility about electrode design.
These two aspects do not have that much in common...

@dor123 It wouldn't hurt anyone to try, Dor.

T5 fills tend to be a bit complex, and vary a lot between different manufacturers. Based on the design of experiments it transpires that there are multiple different compositions that deliver basically the same initial performance.  Occasionally it was found that even though some are identical in terms of initial photoelectric data, there are differences that appear as the lamps age, or in the ignition behaviour, sensitivity to ambient temperature variations, and other effects like arc swirling and snaking.  As a result there were quite frequent changes over time, in search of the optimum conditions.  Same of course for all other parameters like the electrode geometry and emitter coating weight and chemistry.  At some manufacturers the following optimised fills were gradually worked out for T5 types:

T5 Miniature 6W & HO 11W : Argon 1.6mbar
T5 Miniature 8W & HO 15W : Argon 2.1mbar
T5 Miniature 13W & HO 25W : Argon 3.15mbar
T5 Emergency 6W: Cronigen 2.7mbar
T5 Emergency 8W: Cronigen 3.2mbar
T5 FHE 14W: Argon 2.45mbar
T5 FHE 21W: 89:11 Ar:Kr 2.15mbar
T5 FHE 28W: 89:11 Ar:Kr 2.25mbar
T5 FHE 35W: 79:21 Ar:Kr 2.75mbar
T5 FHO 24W: 51:49 Ne:Ar 2.75mbar
T5 FHO 39W: 51:49 Ne:Ar 2.15mbar
T5 FHO 49W: Argon 2.75mbar
T5 FHO 54W: Argon 3.65mbar
T5 FHO 80W: Argon 3.15mbar
T5L8 24W 15in: Argon 2.2mbar
T5L8 28W 2ft: Argon 2.65mbar
T5L8 45W 3ft: Argon 3.45mbar
T5L8 54W 4ft: Argon 4.1mbar
T5L8 80W 6ft: 75:25 Ar:Kr 2.5mbar
T5 FHE Eco 13W: 75:25 Ar:Kr 2.05mbar
T5 FHE Eco 19W: 55:45 Ar:Kr 2.0mbar
T5 FHE Eco 25W: 45:55 Ar:Kr 2.0mbar
T5 FHE Eco 32W: 49:51 Ar:Kr 2.0mbar
T5 FHO Eco 20W: 89:11 Ar:Kr 2.0mbar
T5 FHO Eco 34W: 96:4 Ar:Kr 2.0mbar
T5 FHO Eco 50W: 40:60 Ar:Kr 2.05mbar
T5 FHO Eco 45W: 40:60 Ar:Kr 2.0mbar
T5 FHO Eco 73W: 79:21 Ar:Kr 2.0mbar

Thanks a lot, James.
If 2 tubes were made with the same diameter and same length, same gas filling composition but different gas filling pressure, operated at the same current, am I right to think that the tube with the higher gas filling pressure would have the higher voltage drop? How does it scale, would a tube with 3x the gas pressure have 3x the voltage drop?
What is Cronigen in emergency lighting tubes? Google doesn't seem to know anything about it.