A real dumb Tube question

Ok ok ok, chances are i will get the moron of the evening award for this post, but i have never heard OR seen a tube amplifier in action....

uhm...

do the tubes glow?

I KNOW I SAID IT WAS A DUMB QUESTION! STOP LAUGHING ALREADY!
:)

Seriously. I have 0 experience with tube amps.
do they... ya know... glow?