Pumbas Nakasak
Heading for the great escape.
First off, I didn't say that. Secondly, as I explained, in the context of a laser light show it's a negligible effect.
Physics is all about ignoring negligible effects in the context of a particular problem.
Perhaps I misread but I believed the way you worded your initial response to Dave to be that vapour is a gas and gas has no impact on how light travels, period, and that to me looked like a bit of an over generalisation. If that is not the case Ill be sure to read posts more contextually in future.