I guess the blackening retains heat and IR light, so to melt the glass it rises to around... 600°C

I've seen this several times on LG and GOL with those wedge-base low voltage lamps...is this common?
Was this pic taken under a green traffic light or clear MV?

@Vince 600°C , I usually only see bubbled glass on smaller automotive bulbs so I guess the blackening and the smaller bulb tends to trap enough heat that the glass melts.

@Andy I'm not sure but I also remember reading that others have had the same problem. The pic was taken under a green traffic light.

That makes sense if it only happens on small bulbs...since the heat gets trapped...
BTW what do you think of my new profile pic? I know, it's not lighting related...

Yeah did you see mine? Its in my gallery real bulged

Whoa Does it still work?

I sorta doubt it but maybe

I see this on cheap knockoff bulbs, where the glass used is very low melting, and will deform with the high pressure and temperature inside the lamp. I would guess these are nitrogen filled lamps, as they certainly have a poor efficiency as it is. On H3 lamps it is scary how it bulges and sags from this on the fakes. Ordinary soda glass instead of quartz glass.

Nope, it dosen't work, the filament is actually completely detached from the wires.

Wow good thing nobody touched that in it's final moments!

@Joe: