If you turn on a fluorescent tube-lamp, it flickers before lighting up.
If you then turn it off and turn it back on after 2 seconds, this time it doesn't flicker but lights up straight away.
If you wait for some time (say 10 minutes) and switch on the light again, it flickers before lighting-up, again.
Why does it flicker before lighting up?
And why doesn't it after a 2 seconds gap in turning it on and off?