I found a short article with the presentation of an "OSIRA" lamp in the magazine "BUILDING" from 1938.


Source: BUILDING, N° 1, January 24, 1938



Source: BUILDING, N° 1, January 24, 1938

I wondered if that was the first type of lamp MAF/V 400. Was it only later that the isothermal outer bulb shape was chosen?

Thank you Olav.
My understanding is that the BT-165 isothermal type was introduced first.  As the article describes, this presented mechanical and optical challenges in luminaires that could not accept such a large lamp.  So the TT-120 cylindrical bulb was later introduced to partially overcome those problems.