Just for fun

[mr_big]

What would happen if you dipped just the tube portion of a compact fluorescent bulb into ice water

[Mónico González]

If the tube cracks in any point, just the water (I guess) will go sucked into the tube, where almost instantly will become solid ice, due to the reduced pressure within it.
This would happen, of course, if the water were at near 0? C.
I've seen these same phenomenon in mineral gasified (soda) water bottles that have been into the freezer at 0? C.
When the bottle are tight closed, the inner pressure (about 2 atm.) does not allow the water could be frozen, but when the bottle are opened, its inner pressure equals those of the outer atmosphere, giving as a result that the water begins to cristalyze until the whole mass are turned to a solid block of ice.
But please, if I'm wrong, please, tell me.
Regards.

[Zelandeth]

Provided the tube didn't crack, the light output would just drop appreciably.  Other than that I doubt that there would be anything particularly spectacular to observe.

[mr_big]

what about touching an ice cube to the glass

[Zelandeth]

Depends on a few variables.  Temperature of the glass, how high a thermal expansion coefficient it has, and how much it can flex without breaking.

If the lamp was cold, 99.9% chance nothign would happen.

If the lamp was hot, it's possible it would crack, CFL's don't run terribly hot though, so it'd probably survive even then.

[pSlawinski]

I can say from experience that the tube will likely not crack.  I took one of those air dusters filled with a liquid propellent and sprayed the liquid on a small portion of the tube and all that happened is taht the spot where the tube was sparayed got slightly dim.