I saw them twice while I was living in Canada.
It is an amazing thing to have witnessed and we sat up for hours on the deck watching them.
I would say though that they are not typically how you've likely seen them before, which is the first thing you realise.
More often than not, nature programmes tend to use sped up time-lapses, which makes them move at great speed.
Still photos, like the one posted above, and the ones I took myself, obviously require long exposures, so they end up being brighter and more saturated than how it really looks to your eye.
How I remember seeing them is a dark green glow on the Horizon. It would then all of a sudden occasionally shift.