Just scratching around for an idea here. Wondering if T5s of 28 or 54 watts would work on electronic T8 ballasts of either IS or RS?

No plans in the immediate future for this stuff but just wondering as I may design some neat fixtures for T5s.

Just scratching around for an idea here. Wondering if T5s of 28 or 54 watts would work on electronic T8 ballasts of either IS or RS?

No plans in the immediate future for this stuff but just wondering as I may design some neat fixtures for T5s.

Only speaking for the European F28W/HE and F54W/HO... there are multi-watt electronic ballasts which runs all sorts of lamp types from F36W/T8 to the here meant 28/54W/T5 including other ballast - lamp combinations.
But if the ballast is only for T8 so I don’t think it will run the T5 on proper specs

28W and 54W T5 won't run on American T8.

Some of the T5 HO's are not too far off from the specs of similar PL-L lamps. In particular i think 54W is close. Can you get PL-L ballasts ?

Also, you can use European 230V electronic ballasts wired to 240V (will most likely also work ok with 208V), or us them with a step up transformer from 120V

You might hit the arc curent of HE with some very underdriving ballast or of HO with some very underdriving ballast with 2 outputs parallelled, but i'm not sure how well would the lamps last with Instant Start treatment (they were never meant for such use in Europe, so might have less sturdy cathodes than US T8), and with RS the preheating current may not match

28W and 54W T5 won't run on American T8.

Actually yes they will 'run on them', just not at the correct power-level

  Wondering if T5s of 28 or 54 watts would work on electronic T8 ballasts of either IS or RS?

If you wire a 2xF32 IS ballast for overdrive of a single lamp, you can run either a F54T5 or F40T12 at something pretty close to its normal power.
but...the lack of EOL protection can cause the bad end of a T5 to crack completely off, if you run the lamp all the way to EOL

A 2xF40 electronic RS should also run a single F54 close to normal, but it must be one that... (A) can run lamps shorter than 4', and (B) runs the lamps in series. (in this case, you'd skip the yellow wires, & run a single F54 between the red/blue)

A F32 ballast with low-ballast-factor might run a F28T5 with only a minor overdrive (must be one that supports 5-foot F40T8 or you'll overdrive the ballast)

i'm not sure how well would the lamps last with Instant Start treatment

They do make instant-start T5 HO ballasts here in the US, problem is if they don't have EOL protection, the lamp ends can crack when it goes EOL - I've seen where that's happened in garden places.
(I have a F54 grow light bought used/cheap that came with IS ballasts...one was dead, I replaced them all with programmed-start)