I'm creating fireflies for a movie and I want them to turn on when they move up in y position. Each firefly is an optical flare that is parented to a null with a wiggle expression on the position. I haven't done a lot of in depth work with expressions and can't seem to crack this one. Could so one please offer some advice or an expression that's worked for them? Worse comes to worse I'll do it the old fashioned keyframe way.