They’re working out the kinks. Rainbow-sparking whips are taking the festival world by storm — and becoming family-friendly in spite of their BDSM origins. Dazzling from the handle, users push a button to make the tail light up like a psychedelic jellyfish. The first fiber-optic whip maker has sold 10,000 and predicts a 20 percent summer boost, partly thanks to the mainstreaming of S&M culture. While other light-up dance accessories have been associated with injuries, these have yet to hurt anyone, giving manufacturers a chance to whip up profits.