@leni it's deceptively simple: I have red, blue and green fairy lights in my conservatory. In the dark I zoomed and focussed on them, then moved the camera as I pressed to take the shot. I swirled it in loops but try all sorts of movements. Its like a less-brave - or maybe just less crazy - version of camera tossing (google it). This works well on lights in the distance too - I've had pleasing results from a long-distance lens on the houses across the valley from me, which also picks up street lights and car lights, but did that just as it got dark, not complete darkness
