[morzh]

I tell you this:

My Melodyia radio
http://www.rw6ase.narod.ru/000/rpl_s/melodija_rprl.html
was about 30 years old when we left in 1989 and left it behind (you do not emigrate in the US going through two other countries bringing your monster of a radio with you).
The eye tube, 6E5S (6E5C in Soviet designation) which is octal 6E5, while probably not being super bright anymore, was bright enough, quite green with a very nicely discernible sector.
It was exposed to whatever sunlight we have in all places we lived, and it was always in a brightly Sun-lit rooms.

I am not sure how sunlight could do anything bad enough considering that window glass blocks major part of UV rays.