Hi,
I met a doctor on Helpful Engineering who has no ballast for his UV sterilizing lamp, this one:
https://www.lighting.philips.com/main/prof/conventional-lamps-and-tubes/special-lamps/purificationwater-and-air/residential-water-and-air/tuv-tl-mini/928001104013_EU/product
It is an 8W T5 tube...