Many have heard that arc tubes containing sodium (including both metallic sodium or sodium iodide) will have a shorter life if energized conductors are close to the arc tube wall while it is running. This is believed to be because the sodium ions get attracted to the wall of the arc tube near where the conductor passes, leading to sodium attack.

Methods to prevent this include shielding nearby conductors with nonconductive insulating tubes, having the conductor spaced far away from the arc tube to minimize it's influence, or deenergizing the conductor.

That all makes sense, but how does this actually happen? Why does it happen with sodium iodide as well? Are there any other elements this happens to? Why is it called "photoelectric", how does light play into that?

Thanks!

UV radiation causes electron emission from lamp's metal conductors nearby the arctube. Negative electrons land on the arctube surface and attract positive sodium ions. Sodium atoms are relatively lightweight, so can migrate through hot arctube walls at practically significant speed.

Iodine has heavy atoms and so stays mostly inside, also free iodine does much harm by increasing ignition voltage.

@RRK
Ahh I see, so it literally is the photoelectric effect, I assume this is slightly less of a problem in gas filled envelopes where the electrons can't travel as far. Very interesting, does this happen with mercury or other compounds in lamps or mainly just sodium?

It also happens with lithium.  That is far more corrosive towards quartz even though its chemical reactivity is less than sodium.  The reason is because lithium atoms are smaller and can more easily penetrate deeper into the silica structure.

@James
Thanks! Good to know